Format Issues - will not accept a character or a double

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Chameleon17
Chameleon17 2015-9-25
评论： Thorsten 2015-9-25
Hi,
I'm having another really basic problem.
I want to use a different source for each plant, but it really doesn't like the format.
I get an error message at Xsource saying undefined function X_src_ for function of double or character if I change it. Am I missing something quite obvious?
Any help/advise is very much appreciated!
for plant = 1:5
Xsource = x_src_(num2str(plant));
Ysource = y_src_(num2str(plant)) ;
X_shft = X_rot - x_src_(Xsource);
Y_shft = Y_rot - y_src_(Ysource);
[i] = find(X_shft > 0);

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回答（2 个）

Thorsten
Thorsten 2015-9-25
It would be helpful to know 1) what you want to achieve in your code and 2) how are the variables defined, like x_src_c, X_rot, Y_rot etc.
In particular, what is x_src_? You can check using
whos x_src_
Regardless of what x_src_ actually is, it you try to index into x_src_ using a string, e.g., '1' by using num2str(plant)). That seems strange to me. What do you want to achieve in this line of code?
  2 个评论
Chameleon17
Chameleon17 2015-9-25
Hi, thanks for the answer. I've abandoned the string bit now, it doesn't make sense. I thought it might have been the problem with the double issue I suppose.
I'm just trying to use different locations for each of my plants.
for plants = 1:5
x_src_1 = 0; y_src_1 = 0; x_src_2 = 10000; y_src_2 = 10000; x_src_3 = -10000; y_src_3 = -10000; x_src_4 = 20000; y_src_4 = 20000; x_src_5 = -20000; x_src_5 = -20000;
Xsource = x_src_(plants); Ysource = y_src_(plants);
Thorsten
Thorsten 2015-9-25
Do you mean like this?
for plants = -20000:10000:20000
Xsource = plants; Ysource = plants;
% further code here
end
or if you insists on the order of the plants
for plants = [0 10000 -10000 20000 -20000]
Xsource = plants; Ysource = plants;
% further code here
end

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Guillaume
Guillaume 2015-9-25
From your comment it looks like you're trying to index different variable names depending on a condition. The answer to that is very simple: DO NOT DO THAT. In matlab or any other language.
Create an array and index into this array
X_src = [0, 10000, -10000, 20000, -20000];
Y_src = [0, 10000, -10000, 20000, -20000];
for plant = 1:5
Xsource = X_src(plant);
Ysource = Y_src(plant);
%...
end
Using numbered variables is very poor practice. There are many posts on this forum and a lengthy explanation in the faq detailing why.

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