In an assignment A(I) = B, the number of elements in B and I must be the same.

I need to compute runoff for 2 rainfall conditions

1. If rainfall > 5, then runoff = 1000/CN -10;
2. otherwise Runoff = (Rainfall -0.2 (1000/CN -10))^2 / (Rainfall + 0.80* (1000/CN -10)

My code is as follow

clear
>> Rainfall = randi(10,10,1);
>> CN = randi( 25,10,1);
>> idx = Rainfall > 5;
>> Runoff =size(Rainfall,1);
>> Runoff = zeros(Runoff,1);
>> Runoff(idx)= 1000/CN -10;
 Runoff(~idx) = (Rainfall(~idx) - 0.2 * (1000/CN -10)^2)./Rainfall(~idx) + 0.8 *(1000/CN -10);

I am getting the following error when running the 1st condition

???  In an assignment  A(I) = B, the number of elements in B and
 I must be the same.

Could any body help to solve this issue? I am not very familiar with matlab and trying to write script for runoff calculation using Soil Moisture Condition. Thanks and regards, Saleem

[per isakson]

Readable questions and responses to comments increases the chance to get a useful answer. This time I formatted your text.

Answer 1

[Lessmann]

Hi,

your problem is, that the dimensions of Rainfall and CN don't match. Use the the index idx or ~idx on CN. Also the operators in the last line need tweaking to work elementwise.

Here are the changed lines:

Runoff(idx)= 1000/CN(idx) -10;
Runoff(~idx) = (Rainfall(~idx) - 0.2 * (1000./CN(~idx) -10).^2)./Rainfall(~idx) + 0.8 *(1000./CN(~idx) -10);