MATLAB POLYSPACE RELEASE NOTES Instrukcja Użytkownika Pobierz pdf (Strona 161)

Scripts and Functions

% independent rows or c olumns of a mat rix A.

% RANK(A,tol) is the nu mber of singular values of A

% that are larger than tol.

% RANK(A) uses the default tol = max(size(A)) * norm(A) * eps.

s = svd(A);

if nargin==1

tol = max(size(A)') * max(s) * eps;

end

r = sum(s > tol);

The first line of a function M -file starts with the keyword function.Itgives

the function name and order of arguments. In this case, there are up to two

input arguments and one output argument.

Thenextseverallines,uptothefirstblankorexecutableline,arecomment

lines that provide the help text. These lines are printed when you type

help rank

The first line of the help text is the H1 line, which M ATLAB displays when

you use the

lookfor command or reques t help on a directory.

TherestofthefileistheexecutableMATLABcodedefiningthefunction.The

variable

s introduced in the body of the function, as well as the variables on

the first line,

r, A and tol,arealllocal to the function; they are separate from

any variables in the MATLAB workspace.

This example illustrates one aspect of MATLAB functions that is not

ordinarily found in other programming languages—a variable number of

arguments. The

rank function can be used in several different ways:

rank(A)

r = rank(A)

r = rank(A,1.e-6)

Many M-files work this way. If no output argument is supplied, the result is

stored in

ans. If the second input argument is not supplied, the function

computes a default value. Within the body o f the function, two quantities

named

nargin and nargout are available that tell you the number of input

4-23

1 2 ... 156 157 158 159 160 161 162 163 164 165 166 ... 239 240

Brak uwag

MATLAB POLYSPACE RELEASE NOTES Instrukcja Użytkownika Strona 161