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I'm figuring out complex algebraic calculation in gnu-calc.

Suppose: after many long calculation I got following algebraic expression:

-8 * a - 2 * b + 2 * b * i - 40 * i - 8

and I want the imaginary part of above expression so I do f i (M-x calc-im) .

-8 * im(a) - 2 * im(b) + 2 * re(b) - 40

Of course above is correct, However I want to a,b have a Real Values (i.e. im(a) = 0, im(b) = 0) for further calculations. So desired output for above is: 2 * b - 40.

Question: How to declare variables (in this case a and b) in Real number such that their imaginary part is 0 (for algebraic calculation)?

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According to Gnu-Calc manual 6.6.1: calc-declare-variable (keybinding: s d) is used for declaring variable to be real, int, pos or within range of something e.g [0 .. inf).

In above case:

  • s d a RET real RET: makes variable a to be real
  • s d b RET real RET: makes variable b to be real.

After that, the imaginary part of -8 * a - 2 * b + 2 * b * i - 40 * i - 8 evaluates to 2 b - 40.

Apparently, another more convenient option is calc-edit-Decls (keybinding: s D). It will take you to matrix where you can edit all variable-declarations in one place:

Editing variable ‘Decls’Press ‘C-c C-c’ to finish, ‘C-x k RET’ to cancel.

[ [a, real],
  [b, real],
  [C, pos] ]
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