# Problem-based optimization, Conversion to double from optim.prob​lemdef.Opt​imizationE​xpression is not possible.

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JJ JJ on 18 Dec 2021
Commented: JJ JJ on 26 Dec 2021
Hi,
I have a optimazition problem on DG allocation using mat-power case30, and when I run the code I face the below error:
"The following error occurred converting from optim.problemdef.OptimizationExpression to
double:
Conversion to double from optim.problemdef.OptimizationExpression is not possible.
Error in lossobj (line 8)
mpc.bus(5,3)=mpc.bus(5,3)-PDg
Error in dg_allocation_problemBased (line 6)
prob = optimproblem('Objective',lossobj(PDg));"
clc;
clear all;
PDg = optimvar('PDg','LowerBound',0,'UpperBound',1);
prob = optimproblem('Objective',lossobj(PDg));z
show(prob)
x0.PDg=0;
[sol,fval,exitflag,output] = solve(prob,x0)
function obj=lossobj(PDg)
mpc=case30;
mpc.bus(5,3)=mpc.bus(5,3)-PDg;
mpopt=mpoption('out.all',0,'verbose',0);
results=runpf(mpc,mpopt);
loss=sum(get_losses(results));
obj=real(loss);
the codes files are attached in zip files.
thanks for your help and support.

Alan Weiss on 19 Dec 2021
To use a general nonlinear function with an optimization variable, you must first convert the function to an optimization expression using fcn2optimexpr. For your problem, after defining PDg, enter
expr = fcn2optimexpr(@lossobj,PDg);
prob = optimproblem('Objective',expr);
Then run the optimization.
Alan Weiss
MATLAB mathematical toolbox documentation
JJ JJ on 26 Dec 2021
Thank you Alan for your help and support.
Best regurds
JJ

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