Prerequisites

There are no prerequisites for this example.

About thecompute_averageFunction

Thecompute_average.mfunction uses two persistent variables, the accumulated sum and the number of values added so far, so that you can call the function with one value at a time.

typecompute_average

% y = compute_average(x) % This function takes an input scalar value 'x' and returns the average % value so far. function y = compute_average(x) %#codegen assert(isa(x,'double')); % Input is scalar double % Declare two persistent variables 'sum' and 'cnt'. persistent sum cnt; % Upon the first call we need to initialize the variables. if isempty(sum) sum = 0; cnt = 0; end % Compute the accumulated sum and the number of values so far. sum = sum + x; cnt = cnt + 1; % Return the current average. y = sum / cnt;

The%#codegendirective indicates that the MATLAB code is intended for code generation.

Generate the MEX Function

First, generate a MEX function using the commandcodegenfollowed by the name of the MATLAB file to compile.

codegencompute_average

By default,codegengenerates a MEX function namedhello_world_mexin the current folder. This allows you to test the MATLAB code and MEX function and compare the results.

Run the MEX Function

(10 + 20 + 100) / 3 = 43.3333

compute_average_mex(10)

ans = 10

compute_average_mex(20)

ans = 15

compute_average_mex(100)

ans = 43.3333

Clear the Internal State of Persistent Variables

Clear the persistent variables by using theclear mexcommand.

clearmex

Run the MEX Function Again to Calculate the Average of a Different Set of Values

(10 + 20 + 30 + 40) / 4 = 25

compute_average_mex(10)

ans = 10

compute_average_mex(20)

ans = 15

compute_average_mex(30)

ans = 20

compute_average_mex(40)

ans = 25