Thread Subject:

Indexing error

Hello,
I am receiving this error message for the LAST line of this code. "??? In an assignment A(I) = B, the number of elements in B and I must be the same."

%Start of program
clear all
close all
clc
InfilDepth = 0.001*ones(10,12); %Cumulative Infiltration Depth
AntecedentMoisture = 0.4*ones(10,12);
InitialAntecedentMoisture = 0.3*ones(10,12);
dIdt = zeros(10,12);
del_t =1;
Lambda = 0.23;
SatMoisture = 0.6*ones(10,12);
ResidMoisture = 0.1*ones(10,12);
AirEntry = 0.4;
HydCond = 1e-7;
% Update the Cumulative Infiltration Depth
InfilDepth = InfilDepth + dIdt*del_t; % from definition of dIdt
wf =(AirEntry./((AntecedentMoisture - ResidMoisture)./(SatMoisture - ResidMoisture)).^(1/Lambda)); %Wetting Front suction head
dIdt(AntecedentMoisture >= 0.3*SatMoisture + 0.7*InitialAntecedentMoisture) = HydCond;
%This is the line MATLAB has a problem with:
dIdt(AntecedentMoisture < 0.3*SatMoisture + 0.7*InitialAntecedentMoisture) = HydCond./(1-exp(-InfilDepth./((SatMoisture - AntecedentMoisture).*wf)));

What am I doing wrong?
Thanks!

> dIdt(AntecedentMoisture < 0.3*SatMoisture + 0.7*InitialAntecedentMoisture) = HydCond./(1-exp(-InfilDepth./((SatMoisture - AntecedentMoisture).*wf)));


My guess is that your matrices that you are using the ./ operator on are not the same size. Check to make sure that '-InfilDepth' and '((SatMoisture - AntecedentMoisture).*wf))' are matrices of the same size.

They are of the same size. If fact, the whole RHS is of the same size as the expression in () on the LHS which is what makes the error message, well, interesting.
Thanks for the suggestion.

> dIdt(AntecedentMoisture < 0.3*SatMoisture + 0.7*InitialAntecedentMoisture) = HydCond./(1-exp(-InfilDepth./((SatMoisture - AntecedentMoisture).*wf)));

Looked at it harder and I think I know your problem.

The number of values in I or 'AntecedentMoisture < 0.3*SatMoisture + 0.7*InitialAntecedentMoisture' is variable depending on the logical condition.

The number of values in B is set to a 10x12 matrix. So unless every single value in dldt meets the logical condition then you should run into that error.

-Garrett

"Oluwa KuIse" <wespeakforex@yahoo.com> wrote in message
news:i1fg4e$g1r$1@fred.mathworks.com...
> They are of the same size. If fact, the whole RHS is of the same size as
> the expression in () on the LHS which is what makes the error message,
> well, interesting.
> Thanks for the suggestion.

The error message is _slightly_ misleading. Since you're performing logical
indexing on that line, the number of elements on the right-hand side must be
equal to the number of _nonzeros_ in the logical indexing expression on the
left-hand side (or the right-hand side must be a scalar, using scalar
expansion, or the explicit empty [] to delete elements.) I'll note that to
the developers.

--
Steve Lord
slord@mathworks.com
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