3D matrix from 2D matrix multiplied by 1D array

Question

Karl Zammit 2022-2-19

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1653855-3d-matrix-from-2d-matrix-multiplied-by-1d-array

评论： Karl Zammit 2022-2-20

采纳的回答： Voss

I have a 26 by 5 matrix and want to perform an operation via a 1D array of four entries as follows:

% constants

par_a = {0.043 0.0586 0.1344 0.2056};

par_b = {0.74 0.72 0.66 0.63};

divnum2 = 25;

X2=xo:((xf-xo)/divnum2):xf;

N3 = length(X2);

for i6 = 1:N3

x = X2(i6);

% radial coordinate

r = x*b;

% Rephi calculation at each interval

for i4 = 1:N2

Re_Phi {i6,i4} = (omega{i4}*(r^2))/nu;

end

Re_phi = cell2mat(Re_Phi);

for i6 = 1:N3

for i2 = 1:length(Ctflow)

Nu_r{i2} = par_a{i2} * (Re_phi.^par_b{i2});

end

However I am being met with this error:

Unable to perform assignment because brace indexing is not supported for variables of this type.

How can I go abot it and how can I then call a row or column of values from the resulting 3D matrix??

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Answer 1

Voss 2022-2-20

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1653855-3d-matrix-from-2d-matrix-multiplied-by-1d-array#answer_900165

在 MATLAB Online 中打开

My guess is that Re_Phi and/or Nu_r are matrices before this code is run

Re_Phi = magic(4)
Re_Phi = 4×4
    16     2     3    13
     5    11    10     8
     9     7     6    12
     4    14    15     1
omega = {1};
Re_Phi {1,1} = (omega{1}*(1^2))/1
Unable to perform assignment because brace indexing is not supported for variables of this type.

To avoid this error, you can intialize them as cell arrays of appropriate size before the loops that fill them with values, using the cell() function, e.g.:

% constants
par_a = {0.043 0.0586 0.1344 0.2056};
par_b = {0.74 0.72 0.66 0.63};
divnum2 = 25;
X2=xo:((xf-xo)/divnum2):xf;
N3 = length(X2);
% initialize Re_phi
Re_Phi = cell(N3,N2);
for i6 = 1:N3
   x = X2(i6);
   % radial coordinate    
   r = x*b;
   % Rephi calculation at each interval
   for i4 = 1:N2
    Re_Phi {i6,i4} = (omega{i4}*(r^2))/nu;
   end
end
Re_phi = cell2mat(Re_Phi);
% initialize Nu_r
Nu_r = cell(1,length(Ctflow));
for i6 = 1:N3 % not sure what this loop is for; nothing inside seems to depend on i6
   for i2 = 1:length(Ctflow)
     Nu_r{i2} = par_a{i2} * (Re_phi.^par_b{i2});
   end 
end