MATLAB: How to write a mathematical function in Matlab

cell arrayfunction

Can I build an equation which have different components?

variables written in cell array(1×3) such as 'X1' 'X2' 'X3'

exponents written in matrix (3×3 double) e.g [0 .5 -.5; .5 -.5 0; 1 0 .5]

Parameters written in matrix(3×1) e.g [.55;.25;.6893]

can I get equation like

F= .55*X2^.5*X3^-.5+ .25*X1^.5*X2^-.5+.6893*X1^1*X3^.5

Many thanks

Best Answer

MATLAB is a general purpose programming language. You can build up any string you want.

subf = sprintf('*X%d^e%d', [1:3; 1:3]);
formula = ['a1' subf '+a2' subf '+a3' subf];

What you should try to avoid is executing such strings. Dynamic generation of code is error prone.

Related Solutions

MATLAB: Please Help Optimization using PSO

%{


x1+x2+x3+x4+x5 =1000;
x1^2-4x2+5x3^3+x4^4-3.5x5^2 = 300
%}

Notice that x2 is the only variable that appears linearly in the second equation. So rewrite the first equation as

%{
x2 = 1000 - x1 - x3 - x4 - x5
%}

Now substitute that into the second equation

%{
x1^2-4*(1000 - x1 - x3 - x4 - x5)+5x3^3+x4^4-3.5x5^2 = 300
%}

This is a quadratic in x1 (or x5), so solve it for x1

syms x1 x2 x3 x4 x5
eqn = x1^2-4*(1000 - x1 - x3 - x4 - x5)+5*x3^3+x4^4-3.5*x5^2 == 300
eqn = 
X1 = solve(eqn, x1)
X1 =

Now you run two different PSO runs, one substituting 1000 - x1 - x3 - x4 - x5 for x2 and the first of those X1 values for x1; the other run substituting 1000 - x1 - x3 - x4 - x5 for x2 and the second of those X1 values for x1. These runs will not require equality or inequality constraints (unless there are more constraints you did not tell us about.)

The runs you would do would be over 3 variables only, x3, x4, x5, with you having substituted for x1 and x2 in your objective function.

MATLAB: One more : Symbolic math

You want the opposite of the hypothetical str2sym : you want to convert a symbolic expression to a string. In MATLAB, strings are character arrays, so you want to convert to character.

disp(['x1 = ', char(x1)]);

Best Answer

Related Solutions

MATLAB: Please Help Optimization using PSO

MATLAB: One more : Symbolic math

Related Question