Mercurial > hg > octave-nkf
comparison doc/interpreter/stmt.txi @ 6587:00fad3bad2a5
[project @ 2007-04-26 20:23:31 by dbateman]
| author | dbateman |
|---|---|
| date | Thu, 26 Apr 2007 20:23:31 +0000 |
| parents | 3ef1aa12f04c |
| children | c18ed0e7ee41 |
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| 6586:e4ea529efab0 | 6587:00fad3bad2a5 |
|---|---|
| 503 @code{i} is assigned the first element of the range and the body of the | 503 @code{i} is assigned the first element of the range and the body of the |
| 504 loop is executed once. When the end of the loop body is reached, the | 504 loop is executed once. When the end of the loop body is reached, the |
| 505 next value in the range is assigned to the variable @code{i}, and the | 505 next value in the range is assigned to the variable @code{i}, and the |
| 506 loop body is executed again. This process continues until there are no | 506 loop body is executed again. This process continues until there are no |
| 507 more elements to assign. | 507 more elements to assign. |
| 508 | |
| 509 Within Octave is it also possible to iterate over matrices or cell arrays | |
| 510 using the @code{for} statement. For example consider | |
| 511 | |
| 512 @example | |
| 513 @group | |
| 514 disp("Loop over a matrix") | |
| 515 for i = [1,3;2,4] | |
| 516 i | |
| 517 endfor | |
| 518 disp("Loop over a cell array") | |
| 519 for i = @{1,"two";"three",4@} | |
| 520 i | |
| 521 endfor | |
| 522 @end group | |
| 523 @end example | |
| 524 | |
| 525 @noindent | |
| 526 In this case the variable @code{i} takes on the value of the columns of | |
| 527 the matrix or cell matrix. So the first loop iterates twice, producing | |
| 528 two column vectors @code{[1;2]}, follwed by @code{[3;4]}, and likewise | |
| 529 for the loop over the cell array. This can be extended to loops over | |
| 530 multidimensional arrays. For example | |
| 531 | |
| 532 @example | |
| 533 @group | |
| 534 a = [1,3;2,4]; b = cat(3, a, 2*a); | |
| 535 for i = c | |
| 536 i | |
| 537 endfor | |
| 538 @end group | |
| 539 @end example | |
| 540 | |
| 541 @noindent | |
| 542 In the above case, the mulitdimensional matrix @var{c} is reshaped to a | |
| 543 two dimensional matrix as @code{reshape (c, rows(c), | |
| 544 prod(size(c)(2:end)))} and then the same behavior as a loop over a two | |
| 545 dimensional matrix is produced. | |
| 508 | 546 |
| 509 Although it is possible to rewrite all @code{for} loops as @code{while} | 547 Although it is possible to rewrite all @code{for} loops as @code{while} |
| 510 loops, the Octave language has both statements because often a | 548 loops, the Octave language has both statements because often a |
| 511 @code{for} loop is both less work to type and more natural to think of. | 549 @code{for} loop is both less work to type and more natural to think of. |
| 512 Counting the number of iterations is very common in loops and it can be | 550 Counting the number of iterations is very common in loops and it can be |