How can I specify the dimension of a differentiated function?
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I am getting error when I tried to find h_w_net and the error is "Matrix dimensions must agree" at the last line.
The dimension of k_r=500 by 1, PTC=500 by 500, theta=1 by 500. After I differentiated theta (rep by theta_diff) its dimension is 1 by 200.
How can I make dimension of theta_diff 1 by 500?
Thanks
%Here is the code
T=300;
theta = h_bar*w ./ ( exp( (h_bar*w)/(k_B*T) ) - 1 ) ;
theta_diff=diff(theta,T);
%Thermal conductance calculation
h_w_net= (1/4*pi^2) *theta_diff.* k_r .* PTC ;
2 commentaires
Rik
le 27 Jan 2023
Did you really intend to take the 300th derivative? I get the impression you don't really understand what the diff function is doing.
When you put in an array, if will calculate the difference between subsequent values. So it doesn't really find the derivative, as it find the numerical approximation of the derivative on the midpoints.
x = [1 2 3];
y = [7 3 6];
diff(y),corresponding_x=mean([x(1:(end-1)) ; x(2:end)])
Réponses (2)
Walter Roberson
le 27 Jan 2023
diff() is generally successive differences. It is only derivative if the first parameter is sym or symfun, both from the Symbolic Toolbox
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