Why has my function returned zero?

Question

Daniel Fonsêca 2018-12-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/434281-why-has-my-function-returned-zero

编辑： Walter Roberson 2023-3-27

I have a functio which has returned zero sometimes when it must not. I saw the function and it is running normal, but when it pass the values to variables, they are zero.

A is a column vector with more than 1000 lines. This is the input

function [amf,pf,wf]=la(A)
        %pks vetor com os picos
        %locs vetor com as  localizações
        %w  vetor com as larguras
        [pks,locs,w] = findpeaks(A,'Annotate','extents','WidthReference','halfheight'); 
        %'findpeaks' função que indica os picos e comprimentos dos picos.
        tm = size(pks);
        m = 0;
        %Variáveis usadas para armazenar as amplitudes (am), picos (p) e larguras (we). 
        am1 =0;
        p1 = 0;
        we1 = 0;
        am2 =0;
        p2 = 0;
        we2 = 0;
        
       for x = 1:tm(1,1) %Analisando os picos maiores que 1000
            if 1000 < pks(x,1)
                m = m+1;   
                am1(m,1) = pks(x,1);
                p1(m,1) = locs(x,1);
                we1(m,1) = w(x,1);
            end
       end
       
%Agrupando os picos ao redor do maior valor
v=0;%indica a quantidade de elementos formando o pico
u=1; %indica a quantidade de picos
indice=0; %Armazena os indices dos picos 
tm = size(p1);
    for x=tm(1,1):-1:2 %For para analisar as difrenças de posições
       a= p1(x,1) - p1(x-1,1);
       if a<200 %Se a diferença for menor que 200 canais, agruparemmos os indices na variável indice
        v=v+1;
        indice(v,u)= x;
        indice(v+1,u) = x-1;       
       else
           u=u+1; v=0;
       end
    end
    tm=size(indice);
    if tm(1,1)>1       
    %For para analisar qual maior pico dentro de um grupo
     for u=1:tm(1,2)
        for v=1:tm(1,1)-1
             i = indice(v,u);
            if am1(i,1)<am1(i-1,1)
                 am2(u,1)=am1(i-1,1);
                 p2(u,1)=p1(i-1,1);
                 we2(u,1)=we1(i-1,1);
                            
             end
         end
     end
    
    end
    
    tm=size(am2);
    %analisando entre os picos, qual é o último
    if tm(1,1)>1
        for x=1:tm(1,1)-1
            if p2(x,1)<p2(x+1,1)
                amf=am2(x+1,1);
                pf=p2(x+1,1);
                wf=we2(x+1,1);
              
            end
        end
    else  %Caso tm(1,1) seja igual a 1
         amf=am2(1,1);
         pf=p2(1,1);
         wf=we2(1,1);
    end
    
end

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Rik 2018-12-6

Everything depends on your input. Please make sure we can independently run your code and reproduce the issue.

madhan ravi 2018-12-8

upload A(input) as a text file to test

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Answer 1

Cris LaPierre 2018-12-7

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https://ww2.mathworks.cn/matlabcentral/answers/434281-why-has-my-function-returned-zero#answer_350983

编辑：Cris LaPierre 2018-12-7

在 MATLAB Online 中打开

Is your code returning 0 or empty? Since we don't know anything about your input, here are some suspicious things to look into.

You create am2, p2, we2 and set them equal to zero at the top. There are two obvious scenarios when 0 is returned. When tm(1,1) == 1. This happens when size(p1,1) < 3 or when size(am2,1) == 1.

I also see that your code does not assign any values when p2(x,1)>=p2(x+1,1).

if p2(x,1)<p2(x+1,1)

That might be another area to investigate.

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Daniel Fonsêca 2018-12-8

It returns 0.

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Answer 2

Manuel Infante Francés 2023-3-26

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/434281-why-has-my-function-returned-zero#answer_1201289

To me the same thing happens to me. I have a matrix A of (6x501) and I want to get a vector (3006x1) with all the columns of A next to each other. The last row of all the columns of A are negative numbers and the function returns zeros in the rows that are multiples of 6 of the obtained vector. I attach the code. I would appreciate any help in that regard.

function y = fcn(a,b,c,d,e,f)

y=[a b c d e f]';

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Walter Roberson 2023-3-27

在 MATLAB Online 中打开

function y = fcn(a,b,c,d,e,f)
    assert(isfloat(a), 'a must be float')
    assert(isfloat(b), 'b must be float')
    assert(isfloat(c), 'c must be float')
    assert(isfloat(d), 'd must be float')
    assert(isfloat(e), 'e must be float')
    assert(isfloat(f), 'f must be float')
    y=[a b c d e f]';
    y=y(:);
end

Manuel Infante Francés 2023-3-27

编辑：Walter Roberson 2023-3-27

在 MATLAB Online 中打开

Thank you Mr. Walter. Indeed, the solution provided by you gives the desired value. But, I must say and also thank Mr. Torsten's solution:

function y = fcn(a,b,c,d,e,f)
y=[a b c d e f]';
y=y(:);
end

After reviewing the model many times, I have realized that the vector (f) that entered the function was not the one that should enter (supposedly with negative values) but one with values equal to zero. My apologies for the confusion and thanks again.

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