Output argument ‹variable› (and maybe others) not assigned during call to ‹function›

When I run my script, I get this error from my function. I can't see why

This is my function:

function pdf = apost(m);

sd1 = 300^2;
A = sd1*ones(1,12);
C_m = diag(A);
Cm = inv(C_m);

sd2 = 1;
B = sd2*ones(1,12);
C_d = diag(B);
Cd = inv(C_d);

[N,~] = size(m);
if N==5
    Cm = inv(C_m);
    Cd = inv(C_d);
    m0 = [210.540977721001,336.865564353602,437.925233659682,516.527198675522,572.671459401123,599.339983245783,595.129163691363,574.075065919263,523.545231266222,442.136053214102,305.986220954521,179.661634321921];
    g = [-5.57961065006546,-9.24249212739290,-13.3900010001821,-17.3638621584906,-20.6030599093808,-22.2586614660132,-21.9922416252264,-20.6883184326565,-17.7504996477641,-13.5862938793517,-8.19100512552534,-4.94137181487074]
    y = [-15.0 -24.0 -31.2 -36.8 -40.8 -42.7 -42.4 -40.9 -37.3 -31.5 -21.8 -12.8];
    L = (y-g)'.*C_d.*(y-g);
    rho = (m-m0)'.*Cm.*(m-m0);
    sigma = -0.5.*(rho + L);
else

    disp('Incorrect dimension of input vector')
    
end

This is my script:

% (4) Metropolis algorithm

K = 10000;                      %Number of samples
pts = zeros(length(m0),K);     %Array with sample output points
hfuncval = zeros(1,K);            %Array with function value outputs
pts(:,1) = m0;                  %Set starting points
hfuncval(1) = apost(pts(:,1));     %Compute function in starting point
step = 0.5;                    %Set step length

return
%Start sampling
for k = 2:K
    ptpert = pts(:,k-1) + (2*rand(12,1)-1)*step;         % propose perturbed point
    hfuncpert = sigma(ptpert);                          % Compute function in perturbed point
    u = rand;                                           % Generate random number in [0,1]
   if u < hfuncpert/hfuncval(k-1)                       % accepting new points
   % if u < exp(log(hfuncpert)-log(hfuncval(k-1)))
        pts(:,k) = ptpert;
        hfuncval(k) = hfuncpert;
   else                                                 % Rejecting new points
        pts(:,k) = pts(:,k-1);
        hfuncval(k) = hfuncval(k-1);
    end    
end

[Stephen23]

You defined the function with one output argument, named pdf:

function pdf = apost(m);

But inside the function you did not define pdf anywhere. You need fo define that varaible somwhere in your code if you want it as an output argument, i.e.:

function pdf = apost(m);
...
pdf = ...
end

Note that your code has many unused variables and many warnings shown in the MATLAB Editor: do NOT ignore those warnings! Without checking those warnings your code is very unlikely to do anything close what you expect it to.

[Jonas Damsbo]

Yes, I can see that when I run my script, I now got the error:

"Unable to perform assignment because the left and right sides have a different number of elements."

For this line:

hfuncval(1) = apost(pts(:,1));

How can I fix that?

My hfuncval is 1x10000, m0 is 1x12 and pts is 12x10000

[Guillaume]

For the line

hfuncval(1) = apost(pts(:,1)

which assigns a value to the scalar hfuncval, the function apost must return a scalar.

The error tells you it doesn't (I suspect it returns a vector the same size as pts(:, 1) so 12x1, but we don't know since you haven't shown us what pdf is).

You need to modify apost so it returns a scalar even when it gets a vector as input, or change that line so it doesn't attempt to store a vector in a scalar.

[Rik]

Just as a side note: this question is related to the previously posted question.

Answer 1

[Allen]

Currently, you have only decleared pdf as an output argument at the start of your function, but have neglected to assign a value to it within the function. You need to define pdf somewhere within your function.

function pdf = apost(m);
sd1 = 300^2;
A = sd1*ones(1,12);
C_m = diag(A);
Cm = inv(C_m);
sd2 = 1;
B = sd2*ones(1,12);
C_d = diag(B);
Cd = inv(C_d);
[N,~] = size(m);
if N==5
    Cm = inv(C_m);
    Cd = inv(C_d);
    m0 = [210.540977721001,336.865564353602,437.925233659682,516.527198675522,572.671459401123,599.339983245783,595.129163691363,574.075065919263,523.545231266222,442.136053214102,305.986220954521,179.661634321921];
    g = [-5.57961065006546,-9.24249212739290,-13.3900010001821,-17.3638621584906,-20.6030599093808,-22.2586614660132,-21.9922416252264,-20.6883184326565,-17.7504996477641,-13.5862938793517,-8.19100512552534,-4.94137181487074]
    y = [-15.0 -24.0 -31.2 -36.8 -40.8 -42.7 -42.4 -40.9 -37.3 -31.5 -21.8 -12.8];
    L = (y-g)'.*C_d.*(y-g);
    rho = (m-m0)'.*Cm.*(m-m0);
    sigma = -0.5.*(rho + L);
    %pdf = 'Assign value during this case'
else
    disp('Incorrect dimension of input vector')
    %pdf = 'This case might require a different value for pdf. eg - pdf = [];
end

end