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Derivative of a function

asked 2015-01-12 05:52:24 -0500

Silvia gravatar image

updated 2015-01-23 15:07:59 -0500

FrédéricC gravatar image

Hi, I've got this two functions:

psi=function('psi',t)
psi_d=function('psi_d',t)
psi=(sin(delta(t))*v(t))/(l*cos(delta(t)))
psi_d=diff(psi)

but it says No differentiation variable specified how can I derivate psi? Please someone help me it's driving me crazy since yesterday!

Thank you very much

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By the way, in general the first thing you should do when you encounter an error like that is to make sure you didn't accidentally make a mistake in the syntax. This help can be gotten by typing diff? and it should tell you then that you need the variable of differentiation, as pointed out below.

kcrisman gravatar imagekcrisman ( 2015-01-12 11:15:30 -0500 )edit

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answered 2015-01-12 06:47:37 -0500

FrédéricC gravatar image

You have to specify the derivation variable t:

sage: diff(psi,t)
v(t)*D[0](delta)(t)/l + sin(delta(t))^2*v(t)*D[0](delta)(t)/(l*cos(delta(t))^2) + sin(delta(t))*D[0](v)(t)/(l*cos(delta(t)))
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Thank you so much!!

Silvia gravatar imageSilvia ( 2015-01-12 06:57:17 -0500 )edit

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Asked: 2015-01-12 05:52:24 -0500

Seen: 125 times

Last updated: Jan 12 '15