## Insert f coefficient in pdetool

### NaN1988 (view profile)

on 23 Apr 2014
Latest activity Commented on by NaN1988

### NaN1988 (view profile)

on 27 Apr 2014
Hi all,
I am using pdetool to solve the following parabolic partial differential equation:
y = parabolic(y0,time,b,p,e,t,c,a,f,d)
I need to indicate that the coefficient f depends on the solution "y" and a constant "F" calculated in the previous step. It is clear how to do it when f depends on (x,y,t), however, I don't know how to introduce another parameter. I would need something like
y = parabolic(y0,time,b,p,e,t,c,a,'fcoeff(y,F)',d)
where fcoeff(y,F) is a user function. However, I keep getting this error
Undefined function or variable 'F'
It only recognizes the variables x,y,t. Any suggestion?

### Bill Greene (view profile)

on 27 Apr 2014

Do you calculate F in fcoeff? If so, you can make it a global variable and it will retain its value between calls to fcoeff.
One complicating factor is that the parabolic function uses the variable time step ODE solver, ode15s, internally. So fcoeff gets called at unevenly-spaced and possibly non-monotonically increasing time points. You may need to save several values of F along with the times where they are computed and select a particular one or interpolate between values to obtain the value of F you need.
Bill

NaN1988

on 27 Apr 2014