[CppAD] pow function

[João Leal]

Hello!

While using CppADCodegen I've noticed that CppAD used multiplications for

   pow(variable, parameter).

For instance, the following model

   Z[0] = pow(u[0], 25);

will produce the following source code in CppADCodegen for forward zero
order:

   var4 = ind[0] * ind[0];
   var5 = var4 * var4;
   var6 = var5 * var5;
   dep[0] = var6 * var6 * var6 * ind[0];

I would expect CppAD to also use the pow function and not all these
multiplications (not sure which is faster though).

and the following for the jacobian:

   var4 = ind[0] * ind[0];
   var5 = var4 * var4;
   var6 = var5 * var5;
   var7 = var6 * var6;
   var8 = ind[0] * var6;
   var9 = ind[0] * var7 + var8 * var6 + var8 * var6;
   var10 = var9 * var5 + var9 * var5;
   var11 = var10 * var4 + var10 * var4;
   jac[0] = var7 * var6 + var11 * ind[0] + var11 * ind[0];

Is there any way to change this behavior without doing significant changes
to CppAD?

Best regards,

João Leal
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