MATLAB: Fixiing a component of input vector in fmincon

fminconoptimization

Hi all,
I am using fmincon to optimize a nonlinear program as:
     fun = @(x)obj_fun(x);
     [w,fval] = fmincon(fun,w0,[],[],[],[],lb,ub,[],options);
I would like to know if there is possible to fix a component of x ?
let's assume x is in R^4 and the third component is fixed to 1. something like this:
     x = (x1,x2,1,x3,x4)

Best Answer

There are multiple options for this (one is to simply fix it within your objective function). The other is to use your equality constraint of the form Aeq*x=beq. Set:
Aeq = [0 0 1 0 0];
beq = 1;
[w,fval] = fmincon(fun,w0,[],[],Aeq,beq,lb,ub,[],options);
The actual constraints are allowed to be violated within a specified tolerance. See the options for fmincon if you would like to control the tolerance.
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