Re-writing expressions

[Alexander Lindsay]

Hi all,

I am taking the derivative with respect to a variable, let's call it x, of a complicated expression, let's call it y. A lot of y' can be rewritten in terms of y. In a very simple case, y = exp(x) => y' = exp(x) = y

When I take diff(y,x), obviously I get exp(x)

Is there a way for me to automatically re-write my answer in terms of y? Something along the lines of expr.rewrite(func) ? It's trivial to do it manually in this case, but for more complicated expressions it would be really neat to be able to automate this

[Aaron Meurer]

In general use expr.subs or expr.replace to replace one expression with another.

Aaron Meurer

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[Alexander Lindsay]

Excellent, thanks!