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# Help

## Introduction to Help

The most useful online help command is DESCRIBE which obtains help on all commands containing a particular string. Here by command we mean a built in operator such as INTEGRATE or FACTOR etc. As a typing short cut you may type `? fact` in lieu of `describe("fact")`

    (%i3) ? inte;

     0: (maxima.info)Integration.
     1: Introduction to Integration.
     2: Definitions for Integration.
     3: INTERRUPTS.
     4: ASKINTEGER :Definitions for Simplification.
     5: DISPLAY_FORMAT_INTERNAL :Definitions for Input and Output.
     6: INTEGERP :Definitions for Miscellaneous Options.
     7: INTEGRATE :Definitions for Integration.
     8: INTEGRATION_CONSTANT_COUNTER :Definitions for Integration.
     9: INTERPOLATE :Definitions for Numerical.
    Enter n, all, none, or multiple choices eg 1 3 : 7 8;

    Info from file /d/linux2/local/share/info/maxima.info:
     - Function: INTEGRATE (EXP, VAR)
         integrates exp with respect to var or returns an integral
         expression (the noun form) if it cannot perform the integration
         (see note 1 below).  Roughly speaking three stages are used:
    ...

In the above the user said he wanted items 7 and 8. Note the `;` following the two numbers. He might have typed `all` to see help on all the items.

## Lisp and Maxima

All of Maxima is of course written in lisp. There is a naming convention for functions and variables: All symbols which begin with a "$" sign at lisp level, are read with the "$" sign stripped off at Macsyma level. For example, there are two lisp functions TRANSLATE and $TRANSLATE. If at macsyma level you enter TRANSLATE(FOO); the function which is called is the $translate function. To access the other function you must prefix with a "?". Note you may not put a space after the `?` since that would indicate you were looking for help!

    (%i1) ?TRANSLATE(FOO);

Of course, this may well not do what you wanted it to do since it is a completely different function.

To enter a lisp command you may use

    (%i1) :lisp (foo 1 2)

or to get a lisp prompt use `to_lisp();`, or alternately type `Ctrl-c` to enter into a debug break. This will cause a lisp break loop to be entered. You could now evaluate $%o2 and view the value of the line label %o2, in its internal lisp format. Typing `:q` will quit to top level, if you are in a debug break. If you had exited maxima with `to_lisp();` then you should type

    MAXIMA>(run)

at the lisp prompt, to restart the Maxima session.

If you intend to write lisp functions to be called at macsyma level you should name them by names beginning with a "$". Note that all symbols typed at lisp level are automatically read in upper case, unless you do something like `|$odeSolve|` to force the case to be respected. Maxima interprets symbols as mixed case, if the symbol has already been read before or at the time it was first read there was not an already existing symbol with the same letters but upper case only. Thus if you type

    (%i1) Integrate;
    (%o1) INTEGRATE
    (%i2) Integ;
    (%o2) Integ

The symbol `Integrate` already existed in upper case since it is a Maxima primitive, but INTEG, does not already exist, so the Integ is permitted. This may seem a little bizarre, but we wish to keep old maxima code working, which assumes that Maxima primitives may be in upper or lower case. An advantage of this system is that if you type in lower case, you will immediately see which are the maxima keywords and functions.

To enter Maxima forms at lisp level, you may use the `#$` macro.

                              (setq $foo #$[x,y]$)

This will have the same effect as entering

    (%i1)FOO:[X,Y];

except that foo will not appear in the VALUES list. In order to view foo in macsyma printed format you may type

    (displa $foo)

In this documentation when we wish to refer to a macsyma symbol we shall generally omit the $ just as you would when typing at macsyma level. This will cause confusion when we also wish to refer to a lisp symbol. In this case we shall usually try to use lower case for the lisp symbol and upper case for the macsyma symbol. For example LIST for $list and list for the lisp symbol whose printname is "list".

Since functions defined using the MAXIMA language are not ordinary lisp functions, you must use mfuncall to call them. For example:

    (%o2)                        FOO(X, Y) := X + Y + 3

then at lisp level

    CL-MAXIMA>>(mfuncall '$foo 4 5)
    12

A number of lisp functions are shadowed in the maxima package. This is because their use within maxima is not compatible with the definition as a system function. For example typep behaves differently common lisp than it did in Maclisp. If you want to refer to the zeta lisp typep while in the maxima package you should use global:typep (or cl:typep for common lisp). Thus

      (macsyma:typep '(1 2)) ==> 'list
      (lisp:typep '(1 2))==> error (lisp:type-of '(1 2))==> 'cons

To see which symbols are shadowed look in "src/maxima-package.lisp" or do a describe of the package at lisp level.

## Garbage Collection

Symbolic computation tends to create a good deal of garbage, and effective handling of this can be crucial to successful completion of some programs.

Under GCL, on UNIX systems where the mprotect system call is available (including SUN OS 4.0 and some variants of BSD) a stratified garbage collection is available. This limits the collection to pages which have been recently written to. See the GCL documentation under ALLOCATE and GBC. At the lisp level doing (setq si::*notify-gbc* t) will help you determine which areas might need more space.

## Documentation

The source for the documentation is in ``.texi'` texinfo format. From this format we can produce the info files used by the online commands `?` and `describe`. Also `html` and `pdf` files can be produced.

Additionally there are examples so that you may do

    example(integrate);
    (%i4) example(integrate);
    (%i5) test(f):=BLOCK([u],u:INTEGRATE(f,x),RATSIMP(f-DIFF(u,x)));
    (%o5) test(f) := BLOCK([u], u :
             INTEGRATE(f, x), RATSIMP(f - DIFF(u, x)));
    (%i6) test(SIN(x));
    (%o6) 						       0
    (%i7) test(1/(x+1));
    (%o7) 						       0
    (%i8) test(1/(x^2+1));
    (%o8) 						       0
    (%i9) INTEGRATE(SIN(X)^3,X);

## Definitions for Help

Function: DEMO (file)
  this is the same as BATCH but pauses after each command line and continues when a space is typed (you may need to type `;` followed by a newline, if running under xmaxima). The demo files have suffix `.dem`

Function: DESCRIBE (cmd)

  This command prints documentation on all commands which contain the substring "cmd". Thus

      (%i1) describe("integ");
       0: (maxima.info)Integration.
       1: Introduction to Integration.
       2: Definitions for Integration.
       3: ASKINTEGER :Definitions for Simplification.
      ..
      Enter n, all, none, or multiple choices eg 1 3 : 2 3;
      Info from file /d/linux2/local/share/info/maxima.info:
      Definitions for Integration
      ===========================

       - Function: CHANGEVAR (EXP,F(X,Y),Y,X)
      ...

  see section Introduction to Help

Function: EXAMPLE (command)
  will start up a demonstration of how command works on some expressions. After each command line it will pause and wait for a space to be typed, as in the DEMO command.

  The name of the file containing the examples is given by the variable manual_demo, which defaults to "maxima.demo".

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