How to optimize an objective function with repect to two variables using fmincon?

I want to maximize this objective function with respect to a and b using fmincon.

max(-90a-90b+540)

subjected to 3<=a ; b<=8

[Torsten]

A typical problem for MATLAB's "linprog":

https://de.mathworks.com/help/optim/ug/linprog.html

Answer 1

[Star Strider]

The general approach to maximising a function is to negate it so the minimum that the optimisation functions find is actually the function maximum.

f = @(a,b) (-90*a-90*b+540);
[ab,fv] = fmincon(@(ab) -f(ab(1),ab(2)), rand(2,1), [],[],[],[],[3 -Inf],[inf 8]);

Problem appears unbounded.

fmincon stopped because the objective function value is less than
the value of the objective function limit and constraints 
are satisfied to within the value of the constraint tolerance.

fprintf('\n\ta  = %23.15E\n\tb  = %23.15E\n\tfv = %23.15E\n\n',ab,fv)

	a  =   1.792516492505127E+12
	b  =  -1.880962606528041E+18
	fv =  -1.692864732610394E+20

The problem appears to not be well-posed.

.

[ANCY S GEORGE]

Ok sir.Thank you

[Star Strider]

As always, my pleasure!