MATLAB: Non linear fitting with constraints

constraintsfittingMATLAB

I have a function that uses 9 inputs (cts(1) to cts (9)) and provides 1 value as result. The function needs 4 parameters (c(1) to c(4)). The code of the function is:
fun = @(c,cts) ((c(1) .* (4-c(4))) ./ (c(2)+c(3) .* 4)) *cts(1,:) +...
((c(1) .* (5-c(4))) ./ (c(2)+c(3) .* 5)) *cts(2,:)+ ...
((c(1) .* (6-c(4))) ./ (c(2)+c(3) .* 6)) *cts(3,:) + ...
((c(1) .* (7-c(4))) ./ (c(2)+c(3) .* 7)) *cts(4,:) + ...
((c(1) .* (8-c(4))) ./ (c(2)+c(3) .* 8)) *cts(5,:) + ...
((c(1) .* (9-c(4))) ./ (c(2)+c(3) .* 9)) *cts(6,:) + ...
((c(1) .* (10-c(4))) ./ (c(2)+c(3) .* 10)) *cts(7,:) + ...
((c(1) .* (11-c(4))) ./ (c(2)+c(3) .* 11)) *cts(8,:) + ...
((c(1) .* (12-c(4))) ./ (c(2)+c(3) .* 12)) *cts(9,:)
I have 11 measured values with each 9 inputs. From this data set I want to fit the parameters c. A condition that applies for only the first row of the input is that
((c(1) .* (4-c(4))) ./ (c(2)+c(3) .* 4)) *cts(1,1) must be greater than ((c(1) .* (5-c(4))) ./ (c(2)+c(3) .* 5)) *cts(2,1). Is there an algorithm which can do that? I already tried lsqcurvefit without this constraint, but the fitted parameters do not follow the condition.
Thank you for your time.

Best Answer

You would have to use fmincon, which will let you specify non-linear constraints.
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