Substituting numerical values without partial evaluation.

asked 2012-11-26 14:31:56 +0200

nholtz
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Given an expression of the form:

   var('x y')
   e = x*y + 1

I would like to be able to substitute numerical values into an expression without it being simplified. I'm not too concerned about seeing it in the notebook, but I would like the latex display to be affected. In other words, I would like the equivalent of:

   latex(e(x=5,y=6))   =>   "5 \times 6 + 1"

Any hope of doing this? I could substitute into the text of the latex, but then I would get "5 6 + 1".

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answered 2012-11-26 15:52:21 +0200

nholtz
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Actually, I found sympy to do almost exactly what I want, with:

   sympy.latex( e, mul_symbol='times', symbol_names=d )

where d is a dictionary of symbols -> numerical strings mappings. sympy might turn out to be just enough for my purposes, though I still would like to know if this is possible with a reasonable (i.e. small ;-)) amount of work in sage, just in case.

Basically I have a small number (3-6) of mostly linear eqns to solve where the variables to solve for are not known ahead of time. I'm generating worked out examples of equilibrium eqns for students.

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Cool! Maybe we should have a `mul_symbol` option as well. Glad sympy was sufficient in this case!

kcrisman ( 2012-11-26 16:28:08 +0200 )edit

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answered 2012-11-26 15:08:10 +0200

kcrisman
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sage: e=x.mul(y,hold=True)+1
sage: e
x*y + 1
sage: latex(e)
x y + 1

In general, hold=True is what you want, though this is a little weird for plus and times.

I think we'd have to override the multiplication latex method to get the \times, though this should be possible.

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