If else condition for the rainfall

I have series of daily rainfall data, computed curve number (CN). To compute runoff, I need to fulfill these two conditions

if Rainfall > 0.2
then Runoff = 1000/CN -10
else
Runoff =( Rainfall -0.2 * (1000/CN -10)^2)/Rainfall + 0.8 *(1000/CN -10)

Could any body suggest code for this? I tried to use following script

Runoff = ones(size(Rainfallinches));
>> idx = Rainfallinches >0.2;
>> Runoff(idx)= (1000* 1/Curvenumber -10);

but this doesnot work Kind regards, Saleem

[EDITED, Jan, copied from a new thread:]

My data is as follow Rainfall CN 8 65 2 66 6 88 8 73 5 63 4 65 6 66 5 88 1 73 2 63 3 65 5 66 1 88 5 73 10 63 4 65 3 66 3 88 4 73 3 63 I want to compute Runoff for the following conditions if Rainfall >10 then Runoff = 1000/CN-10 otherwise Runoff = (Rainfall - 0.2 * (1000/CN -10)^2)/Rainfall + 0.8 *(1000/CN -10) Please suggest me code for that kind of data.

[Jan]

I've formatted your code. Please explain "it does not work" with any details. It is less efficient to guess the problem, when you see it on your screen already.

Please post input data for your code e.g. created by rand, such that we can see the type and the dimensions.

[Jan]

Please do not open a new thread to provide data for an open question. This is too confusing for the readers.

If you post values, please use a form, which can be inserted in Matlab's command window by copy&paste. Only then it is clear to the readers. What are the size and type of the variables Rainfallinches and Curvenumber? And again: Please explain what "it does not work" mean. Give us a chance to help you.

[Eng. Fredius Magige]

Tell us all coefficient as Q=kiA

Answer 1

[Thorsten]

You didn't mention what went wrong; the following code should work for you:

 Rainfall = rand(1,10); % fake some data
 CN = 23; % assume it is a scalar, fake some value

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

[Saleem Sarwar]

Thanks Thorsten for your reply. There seem to be some error in this code. My data is as follow Rainfall CN 8 65 2 66 6 88 8 73 5 63 4 65 6 66 5 88 1 73 2 63 3 65 5 66 1 88 5 73 10 63 4 65 3 66 3 88 4 73 3 63 I want to compute Runoff for the following conditions if Rainfall >10 then Runoff = 1000/CN-10 otherwise Runoff = (Rainfall - 0.2 * (1000/CN -10)^2)/Rainfall + 0.8 *(1000/CN -10) Please suggest me code for that kind of data.

Kind regards, Saleem

[Walter Roberson]

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