Initialize values at time = 0

Question

aroj bhattarai 2020-10-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/622388-initialize-values-at-time-0

评论： aroj bhattarai 2020-10-22

采纳的回答： Alan Stevens

在 MATLAB Online 中打开

Dear Matlab users and experts,

In Fortran,

if (TIME.EQ.ZERO)then
   Dmat         = 0.0;
   Dmat_ant 	= 0.0;
   Thetam 		= 0.0;
   Thetam_ant 	= 0.0;
end

assigns those ZEROS at the beginning of the calculation. Likewise, in Matlab curve fitting, I need to initialze these values to zero at very first value of lambdas = 1.0. Where lambda(:,1) and lambda(:,2) are my two X-axis data and PK2 is Y-axis value to be functionally calculated as shown below. I am a new user to Matlab and it seems the code is not properly checking if conditional statements. Neither those initialized Dmat, Dmat_ant, Thetam and Thetam_ant are displayed in the workspace, nor the code responds if Taum_t >= Taum_max statement. For all values of lambdas, my code computes PK2 = PK2_iso + PK2_aniso which is not correct: after lambdas > 1.8, the else condition with PK2 = (1 - Dmat).*PK2_iso + PK2_aniso should also be computed when Taum_t >= Taum_max.

Can anyone please help me to find where I have mistaken in the code?

Thank you very much in advance.

lambda(:,1)  = [1.0, 1.1, 1.2, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2.00, 2.05, 2.10];   
lambda(:,2)  = [1.0, 1.1, 1.2, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2.00, 2.05, 2.10];   
if (lambda(:,1) == lambda(1,1)) & (lambda(:,2) == lambda(1,2))
   Dmat         = 0.0;
   Dmat_ant 	= 0.0;
   Thetam 		= 0.0;
   Thetam_ant 	= 0.0;
end
Taum_max	= S0dm;
Taum_t = sqrt(2.*WbarISO);
if Taum_t < Taum_max       
    PK2 = PK2_iso + PK2_aniso ;
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 - Dmat).*PK2_iso + PK2_aniso ;
end

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Answer 1

Alan Stevens 2020-10-22

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https://ww2.mathworks.cn/matlabcentral/answers/622388-initialize-values-at-time-0#answer_521268

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You probably want to replace

if (lambda(:,1) == lambda(1,1)) & (lambda(:,2) == lambda(1,2))

by

if (lambda(r,1) == lambda(1,1)) && (lambda(r,2) == lambda(1,2))

where r is the row number.

Your original test produces in a vector of values instead of a single value.

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aroj bhattarai 2020-10-22

Hi Alan Stevens,

Your suggestion with defined 'r' in a for loop

if (lambda(r,1) == lambda(1,1)) && (lambda(r,2) == lambda(1,2))

actually gives those initial ZEROS. But I quickly realized that my irresponsiveness of the second Taum_t >= Taum_max is a different issue which is depending on the initial guess during curve fit. If I am unable to find the solution, I will open a separate topic. Thank you for your help.

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