Using Variable inside For loop Iteration

Question

Sean Farrell 2017-2-15

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编辑： Stephen23 2017-2-15

Hi Folks,

I am trying to use a variable inside a for loop iteration, as seen below in the code I have pasted in. I guess the variables don't quite matter too much, but I will explain a bit. Particle_rad is simply a number and obstnew is a large matrix. i is taken as the row value and ii is taken as the column value of the matrix. Essentially, I want to initialize at (i,ii) and then add the particle_rad value to i in order to place a 3 at the new location. Obviously I get an error when I try to do this, and here is the error: Subscript indices must either be real positive integers or logicals. I understand the error, but I am just wondering if there is any way around this. If anyone requires any more explanation, please let me know.

Thank you, Sean

    if obstnew2(i,ii) == 3
            for j = 1:particle_rad
                obstnew2(i+(particle_rad),j) = 3; 
                obstnew2(i+(particle_rad),-j) = 3;

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Answer 1

Kaushik Lakshminarasimhan 2017-2-15

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You're probably getting the error because of the line obstnew2(i+(particle_rad),-j) = 3. You have "minus j" which makes the index negative.

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Kaushik Lakshminarasimhan 2017-2-15

You can do that as long as i+(particle_rad) is a real positive integer. Are you sure the value of particle_rad is a non-negative integer?

Stephen23 2017-2-15

编辑：Stephen23 2017-2-15

"I cannot add a variable to an index value"

You certainly can add variable to create an index. An index is a variable, just like any other, and can be created by adding other variables, multiplying, or any other numeric operation. Of course the variable when it is used as an index must be a integer greater then zero. A common beginner error is to supply a non-integer value.

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