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Topic: Calculating 1st derivative with a parameter
Replies: 4   Last Post: Jun 14, 2012 10:34 AM

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Christopher Creutzig

Posts: 285
Registered: 2/24/09
Re: Calculating 1st derivative with a parameter
Posted: Jun 14, 2012 10:34 AM
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On 06.05.12 22:14, Wojtek wrote:

> Unfortunately when doing it your way I get an error:
>
> ??? Error using ==> sym.sym>notimplemented at 2653
> Function 'lt' is not implemented for MuPAD symbolic objects.


That was new in 2012a, I believe. You should be able to use ?if
double(focValue) < 0.5? in earlier versions.

> Additionally when I try to display the value of dydx_val I get:
>
> dydx_val =
>
> -(289129866313728*D(ceil)(965535013052404736/3125))/125


I assume one of your input parameters (za, zb, zc, zd) contains a
symbolic ?ceil? expression then. That is not differentiable in the
function sense. You may be able to get further by adding

dydx=subs(dydx,'D(ceil)',0);

after defining dydx. Just double-check that the result in the end looks
reasonable. For the value you showed, that would result in zero ? if
that is not a good result, go back to your problem and clearly state
what the derivative of the ceiling function is supposed to be in this
situation.


Christopher



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