Hi, I have a code in MATLAB which tries to zero detect, i am trying to convert the same to C but i am having trouble loading the data.

While running the program in matlab coder, the value of y is taken to be 1, and it does not go to the for loop.I have attached the file(.mat) from which i am getting the signal. The code is:

%cd 'C:\Users\HP\Desktop\Project Simulation\water\WaterBonePlaneInterface\SimulationResults'
%plot frequency spectrum of pulse transmitted through water in time domain


function [g,h,j,o]=generatezeros
%cd C:\Users\HP\Desktop\Project Simulation\water\WaterBonePlaneInterface\SimulationResults\;
y=coder.load('C:\Users\HP\Desktop\Project Simulation\water\WaterBonePlaneInterface\SimulationResults\B.mat');
%y=[-1 1 1 1 -1 -1 -1 2 3 1 1 1 -1];
g=0;
h=0;
j=0;
o=0;
k=0;
coder.extrinsic('display');
for i = 1:length(y)-1  
    if ((sign(y(i+1)) == 1 && sign(y(i))==-1) || (sign(y(i+1))==-1 && sign(y(i))==1))           
        k=k+1;
        display(k);
        if (k==1)
            g=i;
        elseif (k==2)
            h=i;
        elseif (k==3)
            j=i;
        else (k==4)
            o=i;
        end
end
end
display(length(y));
display(g);
display(h);
display(j);
display(o);

Answer 1

[Kunal Khosla]

I did a abit of experiment and was able to figure out the issue. The lines should be changed to

s=coder.load('C:\Users\HP\Desktop\Project Simulation\water\WaterBonePlaneInterface\SimulationResults\B.mat');

y=s.y;

Then the matlab data is loaded on to the C program.

Answer 2

[Guillaume]

The name of your function generatezeros is very misleading since what that function does is find the first 3 and the last indices where a vector changes sign. It does not generate anything in any way. Considering that there is no comment in your code, at least use a function name that explains what it actually does.

Note that

else (k==4)

is the same as

else
    k == 4  %pointless line that will either print 1 or 0 on the command line

it is not equivalent to

elseif k==4

This else wil be executed for all k greater than 3, each time setting o to the index i. So at the end of the loop o will be the index of the last sign change in the vector. If you meant o to be the 4th one, then that's not what your code does.

In any case, the whole function can be simplify to:

function locations = findzerocross(y)
    %input: y a vector of numbers
    %output: the location of all zero-crossing points
    locations = find(diff(sign(y)) ~= 0);
end

If you want the first four locations, you can then index the returned array

y = coder.load('C:\Users\HP\Desktop\Project Simulation\water\WaterBonePlaneInterface\SimulationResults\B.mat');
zerocrossing = findzerocross(y);
zerocross4 = zerocrossing(1:4);

I know nothing about coder, so no idea what you need to do to make it compile.

Answer 3

[Kunal Khosla]

Thanks a lot. Any one with prior Matlab coder experience.