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# If statement is not correctly operating

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aroj bhattarai on 22 Oct 2020
Closed: MATLAB Answer Bot on 20 Aug 2021
Dear Matlab experts,
I have a simple if statement to execute, however is not responding how I am expecting in a relaxation function. In the attached matlab code, I want my code to respond in two steps:
1. Firstly, initialize some internal variables to ZEROS during first elements of X-data vector, i.e., lambda(1,1) and lambda(1,2): The value of these variables remains ZEROS until a subsequent if statement is fulfilled.
for r = 1
if (lambda(r,1) == lambda(1,1)) && (lambda(r,2) == lambda(1,2))
Dmat = 0.0;
Dmat_ant = 0.0;
Thetam = 0.0;
Thetam_ant = 0.0;
end
end
2. Secondly, I need to compute a function value PK2 which is dependent on an internal variable Dmat = [0, 1] and is calculated fulfilling a if statement:
if Taum_t < Taum_max
PK2(:,1) = PK2_peak1;
PK2(:,2) = PK2_peak2;
PK2(:,3) = PK2_peak3;
else
Taum_max = Taum_t;
Amat = (gdm./S0dm.^2 - 0.5).^(-1);
Dmat = 1 - (S0dm./Taum_t).* exp(Amat.*(1 - (Taum_t./S0dm)));
delDmat = Dmat - Dmat_ant;
Thetam = Thetam_ant + WbarISO.* delDmat;
Dmat_ant = Dmat;
Thetam_ant = Thetam;
PK2(:,1) = (1 - Dmat).*PK2_peak1;
PK2(:,2) = (1 - Dmat).*PK2_peak2;
PK2(:,3) = (1 - Dmat).*PK2_peak3;
end
It means, Dmat is calculated only when Taum_t >= Taum_max, for other cases, Dmat = 0. It applies the same for Dmat_ant, Thetam and Thetam_ant.
Running the existing matlab code gives a continusouly increasing PK2 value which does not fit to the Y-data. In addition, commenting the if statement
%if Taum_t < Taum_max
% PK2(:,1) = PK2_peak1;
% PK2(:,2) = PK2_peak2;
% PK2(:,3) = PK2_peak3;
%else
gives the fitted curve towards X-data vs Y-data plot which is again not correct because Dmat, Dmat_ant, Thetam and Thetam_ant are not initialized to ZEROS at the beginning of the calculation.
aroj bhattarai on 28 Oct 2020
Thank you Sindar for the explanation, for loop over lambda and the followed if statement gave me what I was looking for. The unclear variables you mentioned were all user-defined scalars except . I could have asked you the simple formulation instead of confusing long paragraphs.