+, -, *, /, ^ , Div, Mod , Gcd , Lcm , <<, >> , FromBase, ToBase , Precision , GetPrecision , N , Rationalize , IntLog , IntNthRoot , NthRoot , ContFrac , ContFracList, ContFracEval , GuessRational, NearRational, BracketRational , Decimal , TruncRadian , Floor , Ceil , Round , Pslq .

# Arithmetic and other operations on numbers

Besides the usual arithmetical operations, Yacas defines some more advanced operations on numbers. Many of them also work on polynomials.

+, -, *, /, ^ | arithmetic operations
Div, Mod | division with remainder
Gcd | greatest common divisor
Lcm | least common multiple
<<, >> | shift operators
FromBase, ToBase | conversion from/to non-decimal base
Precision | set the precision
GetPrecision | get the current precision
N | compute numerical approximation
Rationalize | convert floating point numbers to fractions
IntLog | integer part of logarithm
IntNthRoot | integer part of n-th root
NthRoot | calculate/simplify nth root of an integer
ContFrac | continued fraction expansion
ContFracList, ContFracEval | manipulate continued fractions
GuessRational, NearRational, BracketRational | find optimal rational approximations
Decimal | decimal representation of a rational
TruncRadian | remainder modulo 2*Pi
Floor | round a number downwards
Ceil | round a number upwards
Round | round a number to the nearest integer
Pslq | search for integer relations between reals

###

+, -, *, /, ^ -- arithmetic operations

##### Standard library

##### Calling format:

    x+y
    +x

Precedence: 70

    x-y

Precedence: left-side: 70 , right-side: 40

    -x
    x*y

Precedence: 40

    x/y

Precedence: 30

    x^y

Precedence: 20

##### Parameters:

`x` and `y` -- objects for which arithmetic operations are defined

##### Description:

These are the basic arithmetic operations. They can work on integers, rational numbers, complex numbers, vectors, matrices and lists.

These operators are implemented in the standard math library (as opposed to being built-in). This means that they can be extended by the user.

##### Examples:

    In> 2+3
    Out> 5;
    In> 2*3
    Out> 6;

###

Div, Mod -- division with remainder

##### Standard library

##### Calling format:

    Div(x,y)
    Mod(x,y)

##### Parameters:

`x`, `y` -- integers or univariate polynomials

##### Description:

`Div` performs integer division and `Mod` returns the remainder after division. `Div` and `Mod` are also defined for polynomials.

If `Div(x,y)` returns "a" and `Mod(x,y)` equals "b", then these numbers satisfy x=a*y+b and 0<=b<y.

##### Examples:

    In> Div(5,3)
    Out> 1;
    In> Mod(5,3)
    Out> 2;

##### See also:

Gcd , Lcm .

###

Gcd -- greatest common divisor

##### Standard library

##### Calling format:

    Gcd(n,m)
    Gcd(list)

##### Parameters:

`n`, `m` -- integers or Gaussian integers or univariate polynomials

`list` -- a list of all integers or all univariate polynomials

##### Description:

This function returns the greatest common divisor of "n" and "m". The gcd is the largest number that divides "n" and "m". It is also known as the highest common factor (hcf). The library code calls `MathGcd`, which is an internal function. This function implements the "binary Euclidean algorithm" for determining the greatest common divisor:

##### Routine for calculating `Gcd(n,m)`

- if n=m then return n
- if both n and m are even then return 2*Gcd(n/2,m/2)
- if exactly one of n or m (say n) is even then return Gcd(n/2,m)
- if both n and m are odd and, say, n>m then return Gcd((n-m)/2,m)

This is a rather fast algorithm on computers that can efficiently shift integers. When factoring Gaussian integers, a slower recursive algorithm is used.

If the second calling form is used, `Gcd` will return the greatest common divisor of all the integers or polynomials in "list". It uses the identity

Gcd(a,b,c)=Gcd(Gcd(a,b),c).

##### Examples:

    In> Gcd(55,10)
    Out> 5;
    In> Gcd({60,24,120})
    Out> 12;
    In> Gcd( 7300 + 12*I, 2700 + 100*I)
    Out> Complex(-4,4);

##### See also:

Lcm .

###

Lcm -- least common multiple

##### Standard library

##### Calling format:

    Lcm(n,m)
    Lcm(list)

##### Parameters:

`n`, `m` -- integers or univariate polynomials `list` -- list of integers

##### Description:

This command returns the least common multiple of "n" and "m" or all of the integers in the list `list`. The least common multiple of two numbers "n" and "m" is the lowest number which is an integer multiple of both "n" and "m". It is calculated with the formula

Lcm(n,m)=Div(n*m,Gcd(n,m)).

This means it also works on polynomials, since `Div`, `Gcd` and multiplication are also defined for them.

##### Examples:

    In> Lcm(60,24)
    Out> 120;
    In> Lcm({3,5,7,9})
    Out> 315;

##### See also:

Gcd .

###

<<, >> -- shift operators

##### Standard library

##### Calling format:

    n<<m
    n>>m

##### Parameters:

`n`, `m` -- integers

##### Description:

These operators shift integers to the left or to the right. They are similar to the C shift operators. These are sign-extended shifts, so they act as multiplication or division by powers of 2.

##### Examples:

    In> 1 << 10
    Out> 1024;
    In> -1024 >> 10
    Out> -1;

###

FromBase, ToBase -- conversion from/to non-decimal base

##### Internal function

##### Calling format:

    FromBase(base,"string")
    ToBase(base, number)

##### Parameters:

`base` -- integer, base to convert to/from

`number` -- integer, number to write out in a different base

`"string"` -- string representing a number in a different base

##### Description:

In Yacas, all numbers are written in decimal notation (base 10). The two functions `FromBase`, `ToBase` convert numbers between base 10 and a different base. Numbers in non-decimal notation are represented by strings.

`FromBase` converts an integer, written as a string in base `base`, to base 10. `ToBase` converts `number`, written in base 10, to base `base`.

Non-integer arguments are not supported.

##### Examples:

Write the binary number `111111` as a decimal number:

    In> FromBase(2,"111111")
    Out> 63;

Write the (decimal) number `255` in hexadecimal notation:

    In> ToBase(16,255)
    Out> "ff";

##### See also:

PAdicExpand .

###

Precision -- set the precision

##### Internal function

##### Calling format:

    Precision(n)

##### Parameters:

`n` -- integer, new value of precision

##### Description:

This command sets the number of decimal digits to be used in calculations. All subsequent floating point operations will allow for at least `n` digits of mantissa.

This is not the number of digits after the decimal point. For example, `123.456` has 3 digits after the decimal point and 6 digits of mantissa. The number `123.456` is adequately computed by specifying `Precision(6)`.

The call `Precision(n)` will not guarantee that all results are precise to `n` digits.

When the precision is changed, all variables containing previously calculated values remain unchanged. The `Precision` function only makes all further calculations proceed with a different precision.

Also, when typing floating-point numbers, the current value of `Precision` is used to implicitly determine the number of precise digits in the number.

##### Examples:

    In> Precision(10)
    Out> True;
    In> N(Sin(1))
    Out> 0.8414709848;
    In> Precision(20)
    Out> True;
    In> x:=N(Sin(1))
    Out> 0.84147098480789650665;

The value `x` is not changed by a `Precision()` call:

    In> [ Precision(10); x; ]
    Out> 0.84147098480789650665;

The value `x` is rounded off to 10 digits after an arithmetic operation:

    In> x+0.
    Out> 0.8414709848;

In the above operation, `0.` was interpreted as a number which is precise to 10 digits (the user does not need to type `0.0000000000` for this to happen). So the result of `x+0.` is precise only to 10 digits.

##### See also:

GetPrecision , N .

###

GetPrecision -- get the current precision

##### Internal function

##### Calling format:

    GetPrecision()

##### Description:

This command returns the current precision, as set by `Precision`.

##### Examples:

    In> GetPrecision();
    Out> 10;
    In> Precision(20);
    Out> True;
    In> GetPrecision();
    Out> 20;

##### See also:

Precision , N .

###

N -- compute numerical approximation

##### Standard library

##### Calling format:

    N(expr)
    N(expr, prec)

##### Parameters:

`expr` -- expression to evaluate

`prec` -- integer, precision to use

##### Description:

This function forces Yacas to give a numerical approximation to the expression "expr", using "prec" digits if the second calling sequence is used, and the precision as set by `SetPrecision` otherwise. This overrides the normal behaviour, in which expressions are kept in symbolic form (eg. `Sqrt(2)` instead of `1.41421`).

Application of the `N` operator will make Yacas calculate floating point representations of functions whenever possible. In addition, the variable `Pi` is bound to the value of Pi calculated at the current precision. (This value is a "cached constant", so it is not recalculated each time `N` is used, unless the precision is increased.)

##### Examples:

    In> 1/2
    Out> 1/2;
    In> N(1/2)
    Out> 0.5;
    In> Sin(1)
    Out> Sin(1);
    In> N(Sin(1),10)
    Out> 0.8414709848;
    In> Pi
    Out> Pi;
    In> N(Pi,20)
    Out> 3.14159265358979323846;

##### See also:

Precision , GetPrecision , Pi , CachedConstant .

###

Rationalize -- convert floating point numbers to fractions

##### Standard library

##### Calling format:

    Rationalize(expr)

##### Parameters:

`expr` -- an expression containing real numbers

##### Description:

This command converts every real number in the expression "expr" into a rational number. This is useful when a calculation needs to be done on floating point numbers and the algorithm is unstable. Converting the floating point numbers to rational numbers will force calculations to be done with infinite precision (by using rational numbers as representations).

It does this by finding the smallest integer n such that multiplying the number with 10^n is an integer. Then it divides by 10^n again, depending on the internal gcd calculation to reduce the resulting division of integers.

##### Examples:

    In> {1.2,3.123,4.5}
    Out> {1.2,3.123,4.5};
    In> Rationalize(%)
    Out> {6/5,3123/1000,9/2};

##### See also:

IsRational .

###

IntLog -- integer part of logarithm

##### Standard library

##### Calling format:

    IntLog(n, base)

##### Parameters:

`n`, `base` -- positive integers

##### Description:

`IntLog` calculates the integer part of the logarithm of `n` in base `base`. The algorithm uses only integer math and may be faster than computing

Ln(n)/Ln(base)
with multiple precision floating-point math and rounding off to get the integer part.

This function can also be used to quickly count the digits in a given number.

##### Examples:

Count the number of bits:

    In> IntLog(257^8, 2)
    Out> 64;

Count the number of decimal digits:

    In> IntLog(321^321, 10)
    Out> 804;

##### See also:

IntNthRoot , Div , Mod , Ln .

###

IntNthRoot -- integer part of n-th root

##### Standard library

##### Calling format:

    IntNthRoot(x, n)

##### Parameters:

`x`, `n` -- positive integers

##### Description:

`IntNthRoot` calculates the integer part of the n-th root of x. The algorithm uses only integer math and may be faster than computing x^(1/n) with floating-point and rounding.

This function is used to test numbers for prime powers.

##### Example:

    In> IntNthRoot(65537^111, 37)
    Out> 281487861809153;

##### See also:

IntLog , MathPower , IsPrimePower .

###

NthRoot -- calculate/simplify nth root of an integer

##### Standard library

##### Calling format:

    NthRoot(m,n)

##### Parameters:

`m` -- a non-negative integer (m>0)

`n` -- a positive integer greater than 1 ( n>1)

##### Description:

`NthRoot(m,n)` calculates the integer part of the n-th root m^(1/n) and returns a list `{f,r}`. `f` and `r` are both positive integers that satisfy f^n*r= m. In other words, f is the largest integer such that m divides f^n and r is the remaining factor.

For large `m` and small `n` `NthRoot` may work quite slowly. Every result `{f,r}` for given `m`, `n` is saved in a lookup table, thus subsequent calls to `NthRoot` with the same values `m`, `n` will be executed quite fast.

##### Example:

    In> NthRoot(12,2)
    Out> {2,3};
    In> NthRoot(81,3)
    Out> {3,3};
    In> NthRoot(3255552,2)
    Out> {144,157};
    In> NthRoot(3255552,3)
    Out> {12,1884};

##### See also:

IntNthRoot , Factors , MathPower .

###

ContFrac -- continued fraction expansion

##### Standard library

##### Calling format:

    ContFrac(x)
    ContFrac(x, depth)

##### Parameters:

`x` -- number or polynomial to expand in continued fractions

`depth` -- integer, maximum required depth of result

##### Description:

This command returns the continued fraction expansion of `x`, which should be either a floating point number or a polynomial. If `depth` is not specified, it defaults to 6. The remainder is denoted by `rest`.

This is especially useful for polynomials, since series expansions that converge slowly will typically converge a lot faster if calculated using a continued fraction expansion.

##### Examples:

    In> PrettyForm(ContFrac(N(Pi)))

                 1
    --------------------------- + 3
               1
    ----------------------- + 7
            1
    ------------------ + 15
          1
    -------------- + 1
       1
    -------- + 292
    rest + 1

    Out> True;
    In> PrettyForm(ContFrac(x^2+x+1, 3))

           x
    ---------------- + 1
             x
    1 - ------------
           x
        -------- + 1
        rest + 1

    Out> True;

##### See also:

ContFracList , NearRational , GuessRational , PAdicExpand , N .

###

ContFracList, ContFracEval -- manipulate continued fractions

##### Standard library

##### Calling format:

    ContFracList(frac)
    ContFracList(frac, depth)
    ContFracEval(list)
    ContFracEval(list, rest)

##### Parameters:

`frac` -- a number to be expanded

`depth` -- desired number of terms

`list` -- a list of coefficients

`rest` -- expression to put at the end of the continued fraction

##### Description:

The function `ContFracList` computes terms of the continued fraction representation of a rational number `frac`. It returns a list of terms of length `depth`. If `depth` is not specified, it returns all terms.

The function `ContFracEval` converts a list of coefficients into a continued fraction expression. The optional parameter `rest` specifies the symbol to put at the end of the expansion. If it is not given, the result is the same as if `rest=0`.

##### Examples:

    In> A:=ContFracList(33/7 + 0.000001)
    Out> {4,1,2,1,1,20409,2,1,13,2,1,4,1,1,3,3,2};
    In> ContFracEval(Take(A, 5))
    Out> 33/7;
    In> ContFracEval(Take(A,3), remainder)
    Out> 1/(1/(remainder+2)+1)+4;

##### See also:

ContFrac , GuessRational .

###

GuessRational, NearRational, BracketRational -- find optimal rational approximations

##### Standard library

##### Calling format:

    GuessRational(x)
    GuessRational(x, digits)
    NearRational(x)
    NearRational(x, digits)
    BracketRational(x, eps)

##### Parameters:

`x` -- a number to be approximated (must be already evaluated to floating-point)

`digits` -- desired number of decimal digits (integer)

`eps` -- desired precision

##### Description:

The functions `GuessRational(x)` and `NearRational(x)` attempt to find "optimal" rational approximations to a given value `x`. The approximations are "optimal" in the sense of having smallest numerators and denominators among all rational numbers close to `x`. This is done by computing a continued fraction representation of `x` and truncating it at a suitably chosen term. Both functions return a rational number which is an approximation of `x`.

Unlike the function `Rationalize()` which converts floating-point numbers to rationals without loss of precision, the functions `GuessRational()` and `NearRational()` are intended to find the best rational that is approximately equal to a given value.

The function `GuessRational()` is useful if you have obtained a floating-point representation of a rational number and you know approximately how many digits its exact representation should contain. This function takes an optional second parameter `digits` which limits the number of decimal digits in the denominator of the resulting rational number. If this parameter is not given, it defaults to half the current precision. This function truncates the continuous fraction expansion when it encounters an unusually large value (see example). This procedure does not always give the "correct" rational number; a rule of thumb is that the floating-point number should have at least as many digits as the combined number of digits in the numerator and the denominator of the correct rational number.

The function `NearRational(x)` is useful if one needs to approximate a given value, i.e. to find an "optimal" rational number that lies in a certain small interval around a certain value `x`. This function takes an optional second parameter `digits` which has slightly different meaning: it specifies the number of digits of precision of the approximation; in other words, the difference between `x` and the resulting rational number should be at most one digit of that precision. The parameter `digits` also defaults to half of the current precision.

The function `BracketRational(x,eps)` can be used to find approximations with a given relative precision from above and from below. This function returns a list of two rational numbers `{r1,r2}` such that r1<x<r2 and Abs(r2-r1)<Abs(x*eps). The argument `x` must be already evaluated to enough precision so that this approximation can be meaningfully found. If the approximation with the desired precision cannot be found, the function returns an empty list.

##### Examples:

Start with a rational number and obtain a floating-point approximation:

    In> x:=N(956/1013)
    Out> 0.9437314906
    In> Rationalize(x)
    Out> 4718657453/5000000000;
    In> V(GuessRational(x))

    GuessRational: using 10 terms of the
      continued fraction
    Out> 956/1013;
    In> ContFracList(x)
    Out> {0,1,16,1,3,2,1,1,1,1,508848,3,1,2,1,2,2};

The first 10 terms of this continued fraction correspond to the correct continued fraction for the original rational number.

    In> NearRational(x)
    Out> 218/231;

This function found a different rational number closeby because the precision was not high enough.

    In> NearRational(x, 10)
    Out> 956/1013;

Find an approximation to Ln(10) good to 8 digits:

    In> BracketRational(N(Ln(10)), 10^(-8))
    Out> {12381/5377,41062/17833};

##### See also:

ContFrac , ContFracList , Rationalize .

###

Decimal -- decimal representation of a rational

##### Standard library

##### Calling format:

    Decimal(frac)

##### Parameters:

`frac` -- a rational number

##### Description:

This function returns the infinite decimal representation of a rational number `frac`. It returns a list, with the first element being the number before the decimal point and the last element the sequence of digits that will repeat forever. All the intermediate list elements are the initial digits before the period sets in.

##### Examples:

    In> Decimal(1/22)
    Out> {0,0,{4,5}};
    In> N(1/22,30)
    Out> 0.045454545454545454545454545454;

##### See also:

N .

###

TruncRadian -- remainder modulo 2*Pi

##### Standard library

##### Calling format:

    TruncRadian(r)

##### Parameters:

`r` -- a number

##### Description:

`TruncRadian` calculates Mod(r,2*Pi), returning a value between 0 and 2*Pi. This function is used in the trigonometry functions, just before doing a numerical calculation using a Taylor series. It greatly speeds up the calculation if the value passed is a large number.

The library uses the formula

TruncRadian(r)=r-Floor(r/(2*Pi))*2*Pi,
where r and 2*Pi are calculated with twice the precision used in the environment to make sure there is no rounding error in the significant digits.

##### Examples:

    In> 2*Pi()
    Out> 6.283185307;
    In> TruncRadian(6.28)
    Out> 6.28;
    In> TruncRadian(6.29)
    Out> 0.0068146929;

##### See also:

Sin , Cos , Tan .

###

Floor -- round a number downwards

##### Standard library

##### Calling format:

    Floor(x)

##### Parameters:

`x` -- a number

##### Description:

This function returns Floor(x), the largest integer smaller than or equal to x.

##### Examples:

    In> Floor(1.1)
    Out> 1;
    In> Floor(-1.1)
    Out> -2;

##### See also:

Ceil , Round .

###

Ceil -- round a number upwards

##### Standard library

##### Calling format:

    Ceil(x)

##### Parameters:

`x` -- a number

##### Description:

This function returns Ceil(x), the smallest integer larger than or equal to x.

##### Examples:

    In> Ceil(1.1)
    Out> 2;
    In> Ceil(-1.1)
    Out> -1;

##### See also:

Floor , Round .

###

Round -- round a number to the nearest integer

##### Standard library

##### Calling format:

    Round(x)

##### Parameters:

`x` -- a number

##### Description:

This function returns the integer closest to x. Half-integers (i.e. numbers of the form n+0.5, with n an integer) are rounded upwards.

##### Examples:

    In> Round(1.49)
    Out> 1;
    In> Round(1.51)
    Out> 2;
    In> Round(-1.49)
    Out> -1;
    In> Round(-1.51)
    Out> -2;

##### See also:

Floor , Ceil .

###

Pslq -- search for integer relations between reals

##### Standard library

##### Calling format:

    Pslq(xlist,precision)

##### Parameters:

`xlist` -- list of numbers

`precision` -- required number of digits precision of calculation

##### Description:

This function is an integer relation detection algorithm. This means that, given the numbers x[i] in the list "xlist", it tries to find integer coefficients a[i] such that a[1]*x[1] + ... + a[n]*x[n]=0. The list of integer coefficients is returned.

The numbers in "xlist" must evaluate to floating point numbers if the `N` operator is applied on them.

##### Example:

    In> Pslq({ 2*Pi+3*Exp(1), Pi, Exp(1) },20)
    Out> {1,-2,-3};

Note: in this example the system detects correctly that 1*(2*Pi+3*e)+(-2)*Pi+(-3)*e=0.

##### See also:

N .