sympy: trigonometric sum-product identities -


i have expression: sin(x)+sin(y)

there well-known trig identity express product of sin , cos.

is there way sympy apply identity?

simplify , trigsimp nothing.

trigsimp, aristocrates points out, reverse, because sin(x) + sin(y) simpler 2*sin((x + y)/2)*cos((x - y)/2).

trigsimp internally uses algorithm based on paper fu, et. al., pattern matching on various trigonometric identities. if @ source code, identities written out in individual functions (the functions named after sections in fu's paper).

looking @ list of simplifications @ top of file, 1 want 

tr9 - contract sums of sin-cos products

testing out, looks works

in [1]: sympy.simplify.fu import tr9  in [2]: tr9(sin(x) + sin(y)) out[2]:      ⎛x   y⎞    ⎛x   y⎞ 2⋅sin⎜─ + ─⎟⋅cos⎜─ - ─⎟      ⎝2   2⎠    ⎝2   2⎠

we factor these out more user-friendly functions, now, fu.py file pretty documented, if function names not particularly memorable.


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