Matlab function help in simulink model

http://imagesup.net/?di=213769298274

i want to write this function in Matlab Function Box

{
function y = func_name(a)
b=b+a;
y=b;
}

the error is b is not defined

Actually I want write code for integration and derivative block

Answer 1

[Azzi Abdelmalek]

function y = func_name(a)
persistent b
if isempty(b)
 b=0;
end
b=b+a;
y=b;

Look at persistent

[Pramit Biswas]

thank you very much for this quick and very helpful reply

can you help me to code this two block

[Azzi Abdelmalek]

Why do you want to code those blocks?

[Pramit Biswas]

1. Learn: How matlab works, what actually happen on this block? logic/math to program in real time; I know that integration can be written as summation. but that theory not works on real time/simulation mode

2. I want to take "to the power" of the signal:Derivative^variable1