# M. Wester's CAS benchmark and `Yacas`

In his 1994 paper Review of CAS mathematical capabilities, Michael Wester has put forward 123 problems that a reasonable computer algebra system should be able to solve and tested the then current versions of various commercial CAS on this list.

Below is the list of Wester's problems with the corresponding `Yacas` code. "OK" means a satisfactory solution, "BUG" means that `Yacas` gives a wrong solution or breaks down, "NO" means that the relevant functionality is not yet implemented.

`Yacas` version: 1.0.56

- (OK) 50!

      Verify(25!, 15511210043330985984000000);
      Verify(50!, (26***50)*25!);

- (OK) Factorize 50!

      Verify(Factors(50!), {{2,47},{3,22},{5,12},
        {7,8},{11,4},{13,3},{17,2},{19,2},{23,2},
        {29,1},{31,1},{37,1},{41,1},{43,1},{47,1}});

- (OK) 1/2+...+1/10=4861/2520

      Verify(Sum(n,2,10,1/n) , 4861/2520);

- (OK) Evaluate e^(Pi*Sqrt(163)) to 50 decimal digits

      Verify(N(1000000000000*(-262537412640768744 +
        Exp(Pi*Sqrt(163))), 50)> -0.75, True);

- (OK) Evaluate the Bessel function J[2] numerically at z=1+I.

      Verify(N(BesselJ(2, 1+I)),
        0.0415798869+I*0.2473976415);

- (OK) Obtain period of decimal fraction 1/7=0.(142857).

      Verify(Decimal(1/7), {0,{1,4,2,8,5,7}});

- Continued fraction of 3.1415926535.

      Verify(ContFracList(3.1415926535, 6),
        {3,7,15,1,292,1});

- (OK) Sqrt(2*Sqrt(3)+4)=1+Sqrt(3).

      Verify(RadSimp(Sqrt(2*Sqrt(3)+4)), 1+Sqrt(3));

- (OK) Sqrt(14+3*Sqrt(3+2*Sqrt(5-12*Sqrt(3-2*Sqrt(2)))))=3+Sqrt(2).

      Verify(RadSimp(Sqrt(14+3*Sqrt(3+2*Sqrt(5-12
        *Sqrt(3-2*Sqrt(2)))))), 3+Sqrt(2));

- (OK) 2*Infinity-3=Infinity.

      Verify(2*Infinity-3, Infinity);

- (NO) Standard deviation of the sample (1, 2, 3, 4, 5).
- (NO) Hypothesis testing with t-distribution.
- (NO) Hypothesis testing with normal distribution (M. Wester probably meant the chi^2 distribution).
- (OK) (x^2-4)/(x^2+4*x+4)=(x-2)/(x+2).

      Verify(GcdReduce((x^2-4)/(x^2+4*x+4),x),
        (x-2)/(x+2));

- (NO) (Exp(x)-1)/(Exp(x/2)+1)=Exp(x/2)-1.
- (OK) Expand (1+x)^20, take derivative and factorize.

      Factor(D(x) Expand((1+x)^20));

- (BUG/NO) Factorize x^100-1.

      Factor(x^100-1);

  (returns the same expression unfactorized)
- (NO) Factorize x^4-3*x^2+1 in the field of rational numbers extended by roots of x^2-x-1.
- (NO) Factorize x^4-3*x^2+1 mod 5.
- (BUG) Partial fraction decomposition of (x^2+2*x+3)/(x^3+4*x^2+5*x+2).

      Apart((x^2+2*x+3)/(x^3+4*x^2+5*x+2), x);

  (does not obtain full partial fraction representation for higher-degree polynomials, e.g. p(x)/(x+a)^n)
- (NO) Assuming x>=y, y>=z, z>=x, deduce x=z.
- (NO) Assuming x>y, y>0, deduce 2*x^2>2*y^2.
- (NO) Solve the inequality Abs(x-1)>2.
- (NO) Solve the inequality (x-1)*...*(x-5)<0.
- (NO) Cos(3*x)/Cos(x)=Cos(x)^2-3*Sin(x)^2 or similar equivalent combination.
- (NO) Cos(3*x)/Cos(x)=2*Cos(2*x)-1.
- (OK) Define rewrite rules to match Cos(3*x)/Cos(x)=Cos(x)^2-3*Sin(x)^2.

      Cos(3*_x)/Cos(_x) <-- Cos(x)^2-3*Sin(x)^2;

- (OK) Sqrt(997)-997^3^(1/6)=0

      Verify(RadSimp(Sqrt(997)-(997^3)^(1/6)), 0);

- (OK) Sqrt(99983)-99983^3^(1/6)=0

      Verify(RadSimp(Sqrt(99983)-(99983^3)^(1/6))
        , 0);

- (OK) (2^(1/3)+4^(1/3))^2-6*(2^(1/3)+4^(1/3))-6=0

      Verify(RadSimp((2^(1/3)+4^(1/3))^3-6*(2^(1/3)+
        4^(1/3))-6), 0);

- (NO) Ln(Tan(x/2+Pi/4))-ArcSinh(Tan(x))=0
- (NO) Numerically, the expression Ln(Tan(x/2+Pi/4))-ArcSinh(Tan(x))=0 and its derivative at x=0 are zero.

      Ln(Tan(x/2+Pi/4))-ArcSinh(Tan(x));
      D(x)(Ln(Tan(x/2+Pi/4))-ArcSinh(Tan(x)));

- (NO) Ln((2*Sqrt(r)+1)/Sqrt(4*r+4*Sqrt(r)+1))=0.
- (NO) (4*r+4*Sqrt(r)+1)^(Sqrt(r)/(2*Sqrt(r)+1))*(2*Sqrt(r)+1)^(2*Sqrt(r)+1)^(-1)-2*Sqrt(r)-1=0, assuming r>0.
- (OK) Obtain real and imaginary parts of Ln(3+4*I).

      Verify(
        Hold({ {x}, {Re(x), Im(x)}}) @ Ln(3+4*I)
        , {Ln(5),ArcTan(4/3)});

- (BUG) Obtain real and imaginary parts of Tan(x+I*y).

      Hold({ {x}, {Re(x), Im(x)}}) @ Tan(x+I*y);

- (BUG) Simplify Ln(Exp(z)) to z for -Pi<Im(z)<=Pi.

      Verify(Simplify(Ln(Exp(z))), z);

  (no conditions on z are used)
- (NO) Assuming Re(x)>0, Re(y)>0, deduce x^(1/n)*y^(1/n)-(x*y)^(1/n)=0.
- (NO) Transform equations, (x==2)/2+(1==1)=>x/2+1==2.
- (BUG) Solve Exp(x)=1 and get all solutions.

      Verify(Solve(Exp(x)==1,x), {x==0});

  (get only one solution)
- (BUG) Solve Tan(x)=1 and get all solutions.

      Verify(Solve(Tan(x)==1,x), {x==Pi/4});

  (get only one solution)
- (OK) Solve a degenerate 3x3 linear system.

      Verify(Solve({x+y+z==6, 2*x+y+2*z==10,
        x+3*y+z==10}, {x,y,z}), {{x==4-z,y==2,z==z}});

  (the new routine `Solve` cannot do this yet)
- (OK) Invert a 2x2 symbolic matrix.

      Verify(Simplify(Inverse({{a,b},{1,a*b}})),
        {{a/(a^2-1), -1/(a^2-1)},
        {-1/(b*(a^2-1)), a/(b*(a^2-1))}});

- (BUG) Compute the determinant of the 4x4 Vandermonde matrix.

      Factor(Determinant(VandermondeMatrix
        ({a,b,c,d})));

  (this does not factor correctly)
- (OK) Find eigenvalues of a 3x3 integer matrix.

      Verify(EigenValues({{5,-3,-7},{-2,1,2},
        {2,-3,-4}}) , {1,-2,3});

- (OK) Verify some standard limits found by L'Hopital's rule:

      Verify(Limit(x,Infinity) (1+1/x)^x, Exp(1));
      Verify(Limit(x,0) (1-Cos(x))/x^2, 1/2);

- (OK) D(x)Abs(x)

      Verify(D(x) Abs(x), Sign(x));

- (OK) (Integrate(x)Abs(x))=Abs(x)*x/2

    Verify(Simplify(Integrate(x) Abs(x)),
      Abs(x)*x/2);

- (OK) Compute derivative of Abs(x), piecewise defined.

      Verify(D(x)if(x<0) (-x) else x,
        Simplify(if(x<0) -1 else 1));

- (OK) Integrate Abs(x), piecewise defined.

      Verify(Simplify(Integrate(x)
        if(x<0) (-x) else x),
        Simplify(if(x<0) (-x^2/2) else x^2/2));

- (OK) Taylor series of 1/Sqrt(1-v^2/c^2) at v=0.

      S := Taylor(v,0,4) 1/Sqrt(1-v^2/c^2);
      TestYacas(S, 1+v^2/(2*c^2)+3/8*v^4/c^4);

  Note: The result of `Taylor` is not in convenient form but is equivalent.
- (OK) Compute the Taylor expansion of the inverse square of the above.

      TestYacas(Taylor(v,0,4) 1/S^2, 1-v^2/c^2);

  Note: The result of `Taylor` is not in convenient form but is equivalent.
- (OK) (Taylor expansion of Sin(x))/(Taylor expansion of Cos(x)) = (Taylor expansion of Tan(x)).

      TestYacas(Taylor(x,0,5)(Taylor(x,0,5)Sin(x))/
        (Taylor(x,0,5)Cos(x)), Taylor(x,0,5)Tan(x));

- (BUG) Taylor expansion of Ln(x)^a*Exp(-b*x) at x=1.

      //Taylor(x,1,3)(Ln(x))^a*Exp(-b*x);

  (bugs in Deriv manipulation)
- (BUG) Taylor expansion of Ln(Sin(x)/x) at x=0.

      //Taylor(x,0,5) Ln(Sin(x)/x);

  (never stops)
- (NO) Compute n-th term of the Taylor series of Ln(Sin(x)/x) at x=0.
- (NO) Compute n-th term of the Taylor series of Exp(-x)*Sin(x) at x=0.
- (OK) Solve x=Sin(y)+Cos(y) for y as Taylor series in x at x=1.

      TestYacas(InverseTaylor(y,0,4) Sin(y)+Cos(y),
        (y-1)+(y-1)^2/2+2*(y-1)^3/3+(y-1)^4);

  Note that `InverseTaylor` does not give the series in terms of x but in terms of y which is semantically wrong. But other CAS do the same.
- (OK) Compute Legendre polynomials directly from Rodrigues's formula, P[n]=1/(2*n)!! *(Deriv(x,n)(x^2-1)^n).

      P(n,x) := Simplify( 1/(2*n)!! *
        Deriv(x,n) (x^2-1)^n );
      TestYacas(P(4,x), (35*x^4)/8+(-15*x^2)/4+3/8);

- (OK) Compute Legendre polynomials P[n] recursively.

      Verify(OrthoP(4,x)
        , 3/8+((35*x^2)/8-15/4)*x^2);

- (OK) Compute Legendre polynomial P[4] at x=1.

      Verify(OrthoP(4,1), 1);

- (OK) Define the polynomial p=Sum(i,1,5,a[i]*x^i).

      p:=Sum(i,1,5,a[i]*x^i);
      Verify(p, a[1]*x+a[2]*x^2+a[3]*x^3
        +a[4]*x^4+a[5]*x^5);

- (OK) Convert the above to Horner's form.

      Verify(Horner(p, x), ((((a[5]*x+a[4])*x
        +a[3])*x+a[2])*x+a[1])*x);

- (NO) Convert the result of problem 127 to Fortran syntax.

      CForm(Horner(p, x));

- (OK) Verify that True And False=False.

      Verify(True And False, False);

- (OK) Prove x Or Not x.

      Verify(CanProve(x Or Not x), True);

- (OK) Prove x Or y Or x And y=>x Or y.

      Verify(CanProve(x Or y Or x And y => x Or y)
        , True);