Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
NCTM or The Math Forum.



Re: Calculating 1st derivative with a parameter
Posted:
Jun 14, 2012 10:34 AM


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 doublecheck 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



