MATLAB: Change variable value based on other variable in if loop

if statementMATLAB

I have a simple code that takes a user's input, and then changes 2 variables based on that:

var1 = 0;
var2 = 0;
in1 = input('first: ', 's');
in2 = input('second: ', 's');
if in1 = 3 && in2 = 4;
    var1 = 2;
    var2 = 5;
elseif in1 = 6 && in2 = 7;
    var1 = 8;
    var2 = 9;
else 
    disp('invalid input');
end

I didn't really expect it to work, as I was sure I had the syntax wrong. I get the error:

The expression to the left of the equals sign is not a valid target for an assignment.

and I am wondering how I can fix the syntax.

Best Answer

Your input command is requesting a string input:

in1 = input('first: ','s');
in2 = input('second: ','s');

This results in in1 and in2 being strings.

To input them as numbers, simply omit the 's'

in1 = input('first: ');
in2 = input('second: ')'

Also, to perform logical comparrison, use 2 equal signs, e.g.:

if in1 == 3 && in2 == 4

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One way:

str = sprintf('''%s''', usersString)

MATLAB: How to direct the variable in the genetic algorithm function to workspace function

You need to parameterize the objective function, which can be achieved either using an anonymous function or nested functions:

https://www.mathworks.com/help/matlab/math/parameterizing-functions.html

https://www.mathworks.com/help/optim/ug/passing-extra-parameters.html

Method one: nested functions: you could do something like this:

function [x,fval] = myga(v1,v2,v3,v4,LB,UB)
[x,fval] = ga(@myfunc,2,[],[],[],[],LB,UB,@constraint);
  function y = myfunc(x)
    y = x(1)*v1 + x(2)*v2;
  end
  function [c,ceq] = constraint(x)
    c = [x(1)+x(2)-v3;x(1)*x(2)-v4];
    ceq = [];
  end
end

and call it like this:

var1 = str2double(input('Variable 1: ','s'));
var2 = str2double(input('Variable 2: ','s'));
var3 = str2double(input('Variable 3: ','s'));
var4 = str2double(input('Variable 4: ','s'));
[x,fval] = myga(var1,var2,var3,var4,[0,0],[100,100])

Method two: anonymous functions: you could do this (with version R2016b or later, where functions may be defined at the end of a script):

var1 = str2double(input('Variable 1: ','s'));
var2 = str2double(input('Variable 2: ','s'));
var3 = str2double(input('Variable 3: ','s'));
var4 = str2double(input('Variable 4: ','s'));
LB = [0,0];
UB = [100,100];
objfun = @(x)myfunc(x,var1,var2);
confun = @(x)constraint(x,var3,var4);
[x,fval] = ga(objfun,2,[],[],[],[],LB,UB,confun);
function y = myfunc(x,v1,v2)
y = x(1)*v1 + x(2)*v2;
end
function [c,ceq] = constraint(x,v3,v4)
c = [x(1)+x(2)-v3;x(1)*x(2)-v4];
ceq = [];
end

Best Answer

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