Problem with understanding the error

 I have the following code
   function x = mapvariables(x)
data=xlsread('newsections.xlsx'); %reading data from excel file
allx1_2=data(:,1)'; %Extracting all the serial numbers
x(1) = allx1_2(x(1)); 
x(2) = allx1_2(x(2));

allx1_2 is a 1*65 row vector which contains numbers in serial i.e. 1,2,3..65. I am running a genetic algorithm and my variable 'x' takes the value from this discrete set 'allx1_2'. Another file that contains Constraints is:

    function [c, ceq] = ga_constraints(x,Dos)
Lc=5;Lb=12;  %in metre
E = 2e8; % Young's modulus in kN/m^2
deltaMax =Lb/325 ; % Maximum end deflection in m
%sigmaMax =130e3 ; % Maximum stress in each section of the beam in kN/m2
lamcolmax=250; %  Max slenderness limits
lambeammax=180;
x=mapvariables(x);
stress = Dos.ch-1;
% Deflection of the stepped cantilever
deflection = Dos.disp - deltaMax;
% Slenderness ratio constraints
Sl_Ratio = [
    Lc - lamcolmax*Dos.rcol;...
    Lb - lambeammax*Dos.rbeam];
% All nonlinear constraints
c = [stress;deflection;Sl_Ratio];
% No equality constraints
ceq = [];
%fun=@(Dos)ga_constraints(x,Dos); %Anonymous function which will be called
Dos is another function which generates constraints.I have checked Dos and it works fine.My constraints are non linear.when I run GA as

   rng(1,'twister')
[x fval exitflag]=ga(@final_cost,2,[],[],[],[],[],[],@ga_constraints,[1 2])

• It gives following error ; *Error using ga (line 342)Attempted to access allx1_2(-1); index must be a positive integer or logical.

Caused by: Failure in initial user-supplied nonlinear constraint function evaluation. I'm not getting why it is taking (-1) ???? SORRY FOR THE LONG POST..I JUST NEED TO KNOW WHERE AM I GOING WRONG? what is the "Caused by"?

Answer 1

[Image Analyst]

By looking at this: http://blogs.mathworks.com/videos/2012/07/03/debugging-in-matlab/ you will be able to discover why you're passing an index of -1 to allx1_2. Indexes start at 1, not -1 or 0 or any arbitrary number. See the FAQ.

In the lines

x(1) = allx1_2(x(1)); 
x(2) = allx1_2(x(2));

has x been defined yet? It comes in via the argument list. So why are you having either x(1) or x(2) be -1? That's why you're getting an error. x must contain integers like 1,2,3,4,5,..... not -1 (like you have) and not 0 or any negative number.

[Ace_ventura]

x has been defined as function. It has variables x(1) and x(2). TO make sure x(1) takes positive integer ,I have formed the set allx1_2 which contains[1 2 3....65]. x(1) =allx1_2(x(1)) will then map x(1) from this set and should take any positive value. I don't understand from where-1 is coming?

Answer 2

[Star Strider]

Is there more to the error message, like a listing of the exact line throwing the error?

What does this line (and the function it calls)

x=mapvariables(x);

do? Could that be throwing the error? I don’t see where you use ‘x’ anywhere else.

[Ace_ventura]

x has been defined as function. It has variables x(1) and x(2). TO make sure x(1) takes positive integer ,I have formed the set allx1_2 which contains[1 2 3....65]. x(1) =allx1_2(x(1)) will then map x(1) from this set and should take any positive value. I am applying genetic algorithm on this problem. x(1) ,x(2) are my variables. x=mapvariables(x) directs the code to this function so that it takes value from the particular discrete set.

[Star Strider]

What I’m wondering is how the negative index gets created. We need to see the code that’s throwing the error.