Re: Derivative Evaluation

*To*: mathgroup at smc.vnet.net*Subject*: [mg6051] Re: [mg6017] Derivative Evaluation*From*: seanross at worldnet.att.net*Date*: Fri, 14 Feb 1997 01:10:43 -0500*Sender*: owner-wri-mathgroup at wolfram.com

John Cigana wrote: > > Hello, > > I have a 7 parameters multivariate function. i.e. y = f(x1..x7). > > I am able to correctly find the partial derivative for each parameter. > > However, I can't seem to be able to evaluate my derivative at a given > point. i.e. f'(x1=0.01, x2=0.5, x3=0.02, ... x7=0.05) = Value ! > > Any insight on the subject ?? Any help appreciated ! > > Thanks, > > JOHN CIGANA, Mathematica makes it very clumsy to be able to evaluate the results of symbolic calculations as functions. Here is how I have been able to do it. #1-get rid of any curly braces by taking the [[1]] or [[1,1]] etc part of the expression. #2-set the symbolic expression equal to a symbol. #3-set a second symbol with a variable list equal to the first using a transformation rule. Example: suppose your derivative returns: {{x^2 +y^2}} Then, f=%[[1,1]]; ff[a_,b_]:=f/.{x->a,y->b} should give you an evaluatable function. Since I am writing this from memory, I remember that the second line works for = or := but not both. You may have to play a little with the assignment operators. ~ ~ ~ ~ ~ ~ ~ ~