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3 Getting Started with MEX-Files

3-4

The curve ca n be graphed in many ways. Sierpinski's method is:

•Start with a triangle and from it remove a trianglethat is one-half the height

of the original and inverted. This leaves three triangles.

•From each of the remaining three triangles, remove a triangle that is

one-fourth the height of these new triangles and inverted. This leaves nine

triangles.

•The p rocess continues and at infinity the surface area becomes zero and t he

length of the curve is infinite.

gasket.m is a good candidate for compilation because it contains a loop. The

overhead ofthe

for loop command is relatively high compared to the cost of the

loop body. M-file programmers usually try to avoid loops containing scalar

operations because loops run relatively slowly under the MATLAB interpreter.

To achieve a reasonable approximation of the Sierpinski Gasket, set the

number of points to 50,000. To compute the coordinates and time the

computation, you can use

tic; x = gasket(50000); toc

To display the figure, you can use

imagesc(x); colormap([1 1 1;0 0 0]);

axis equal tight

Invoking the M-File

To get a bas eli ne read ing , yo u can determine how long it takes the MATLAB

interpreter to run

gasket.m. The built-in MATLAB functions tic and toc are

useful tools for measuring time.

tic; x = gasket(50000); toc

elapsed_time =

7.9620

On t he Pentium Pro 200, the M-file took about 10 seconds of CPU time to

calculate the first 50,000 points on the Sierpinski Gasket.

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MATLAB COMPILER RELEASE NOTES Guía de usuario Pagina 62