MATLAB: Am I getting “Array indices must be positive integers or logical values” error

array indices;logical valuespositive integers

Array indices must be positive integers or logical values.

Error in A2Q1>LinearConv (line 68)

yc(i) = yc(i) + x1(i-j+1).*x2(j);

function yfnc = LinearConv(x1, x2, len)
    yc = zeros(1, len);
    for i = 1:len
    %Total terms will be 1 to len
        for j = 1:(i+1)
            if(i-j+1<length(x1) && j<length(x2)) 
                yc(i) = yc(i) + x1(i-j+1).*x2(j); 
                %Equation
            end
        end
    end
yfnc = yc;
end

Best Answer

Consider this indexing:

x1(i-j+1)

What value does it have on the last iteration of the j loop? (hint: zero).

i-j+1 % that index
j = i+1 % last iteration
i-(i+1)+1 % substitute j
i-i-1+1 % zero

Related Solutions

MATLAB: How to take 100 samples of a plot.

First, what are you actually doing with M, Xdot1, etc.? Currently, the code overwrites them each N_m loop, without doing anything with the results

Try this: define sampled vectors, so you can later vectorize things:

index=randi([100,499],1,N_m);
x1_samp0 = x1(index);
x1_samp1 = x1(index+1);
...
Xdot1=(x1_samp1-x1_samp0)/dt;
...
M(:,1)=1;
M(:,2)=x1_samp0;
...
M(:,6)=x1_samp0.^2;

edit: changed my mind on other option; don't do it. Here are some general tips, though:

if you have a set of conditions that can be expressed as variable=first, variable=second, etc. -- use a switch instead of if-elseif
If you have a loop running over a set of conditions and operations which have nothing else in common -- just run each line individually, then fill in the "else" portion after

for j=1:N_basis
    if j==1
       M(i,j)=1;
    elseif j==2
       M(i,j)=x1(index(i));
    elseif j==3
       M(i,j)=y1(index(i));
    end
end

does the same as the below, but cleaner and faster:

M(i,1)=1;
M(i,2)=x1(index(i));
M(i,3)=y1(index(i));

many, many, many for loops can be replaced with vector operations. It's kinda the point of Matlab

MATLAB: How to stop this loop

That should stop it, if XN ever exceeds 0.82. Apparently it doesn't though. This is the way to find out why: http://blogs.mathworks.com/videos/2012/07/03/debugging-in-matlab/ Perhaps since you don't pass I into any of the arrays or functions in the first two lines, the values never change. Not sure since we don't have those arrays or functions to check them.

Best Answer

Related Solutions

MATLAB: How to take 100 samples of a plot.

MATLAB: How to stop this loop

Related Question