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# Evaluating the derivative of piecewise functions

Hi,

In Sage 7.5 you can numerically evaluate the derivative of a regular symbolic expression using:

sage: h(x) = sin(x)
sage: diff(h)(2).n()
-0.416146836547142


Old Piecewise functions could be treated in the same way:

sage: g = Piecewise([([0,2], sin(x)), ((2,3), cos(x))])
... DeprecationWarning ...
sage: diff(g)(1).n()
0.540302305868140


However, new piecewise functions don't:

sage: f = piecewise([([0,2], sin(x)), ((2,3), cos(x))])
sage: diff(f)(1).n()
... Error ...


Thanks in advance.

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## 1 Answer

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The new piecewise is unfortunately not very user friendly. Here's one workaround:

diff(f.expression_at(1))(1).n()

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## Comments

Thank you @paulmasson. So that means that piecewise cannot operate as similar as Piecewise does with symbolic expressions. In my opinion this is a drawback.

( 2017-02-10 17:20:56 +0100 )edit

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Asked: 2017-02-04 19:43:29 +0100

Seen: 481 times

Last updated: Feb 05 '17