Question

I am trying to make a program which maps coordinates. I am having trouble getting Matlab to select specific values based on the vector inequality. Maybe I am doing it wrong but here is my code, where g is a vector giving the global locations of the points. EL is the length of “objects” and the local coordinates are the coordinates of the points on the “objects” for a 1-D case. Then those local coordinates are reevaluated to give a value of -1 to 1 across the length of the global object. PL is the location of the objects globally.

%Get the local coordinates of the points

for g=(gp(gp>0))
    for n1=(gp(gp<EL(1,1)))
    gp1=[n1, 1];
    end;
    for x=(gp(PL((x1-1),1)<gp<PL((x1),1)));
    gp2=[(x-(EL(x1,1))),1];
    end
    for x=(gp((PL(x1,1)<=gp)));
    gp3=[((x)-(EL(x1,1))),1];
    end
    lpap=([gp1,gp2,gp3]);
    %use the local coordinates to get the natural coordinates
    for x=(gp(gp<=EL(1,1)))
    nc=[((lpap*2)/EL(1,1))-1,1];
    end
    for x=(gp(PL(x1-1,1)<gp<PL(x1,1)));
    nc1=[((lpap*2)/EL(x1,1))-1,1];
    end
    for p=(gp(PL(x1,1)<=gp));
    nc2=[((lpap*2)/EL(x1,1))-1,1];
    end
    nct=[nc,nc1,nc2]

end

Besides nct not being -1 to 1 I know something is wrong because running this gives me one constant value for the x,p, n1 variables, which should give multiple values.

Answer 1

I’m not sure what you’re trying to do here, and I suggest reading MATLAB’s documentation on flow control to get a better idea of how to program in matlab, but just to get you started…

For loops in matlab work over an array:

for n = 1:10
    % do stuff
end

To select parts of an array based on value, you would use index referencing:

a = [1 2 3 4 5 6 7 8];
a_gt_four = a(a>4);  % returns [5 6 7 8];