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Some folks might think: “you still use RCS”?!? And we will say, hey, at least we switched from SCCS to RCS back in … I think it was around 1994 ... at least we are keeping up! :-) :-) :-) Logs say that SCCS version 18 became RCS version 19 on 1994 March 18. RCS served us well. But now it is time to move on. And so we are switching to git. Calc releases produce a lot of file changes. In the 125 releases of calc since 1996, when I started managing calc releases, there have been 15473 file mods!
141 lines
4.0 KiB
Plaintext
141 lines
4.0 KiB
Plaintext
NAME
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=
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SYNOPSIS
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a = b
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a = {e_1, e_2, ...[ { ... } ] }
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TYPES
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a lvalue, current value a structure in { } case
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b expression
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e_0, e_1, ... expressions, blanks, or initializer lists
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return lvalue (a)
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DESCRIPTION
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Here an lvalue is either a simple variable specified by an identifier,
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or an element of an existing structure specified by one or more
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qualifiers following an identifier.
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An initializer list is a comma-separated list enclosed in braces as in
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{e_0, e_1, ... }
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where each e_i is an expression, blank or initializer list.
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a = b evaluates b, assigns its value to a, and returns a.
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a = {e_0, e_1, ... } where the e_i are expressions or blanks,
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requires the current value of a to be a matrix, list
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or object with at least as many elements as listed e_i. Each non-blank
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e_i is evaluated and its value is assigned to a[[i]]; elements a[[i]]
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corresponding to blank e_i are unchanged.
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If, in a = {e_0, e_1, ...}, e_i is an initializer list, as in
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{e_i_0, e_1_1, ...}, the corresponding a[[i]] is to be a matrix, list
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or object with at least as many elements as listed e_i_j. Depending on
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whether e_i_j is an expression, blank, or initializer list, one, no, or
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possibly more than one assignment, is made to a[[i]][[j]] or, if
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relevant and possible, its elements.
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In simple assignments, = associates from right to left so that, for
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example,
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a = b = c
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has the effect of a = (b = c) and results in assigning the value of c
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to both a and b. The expression (a = b) = c is acceptable, but has the
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effect of a = b; a = c; in which the first assignment is superseded by
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the second.
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In initializations, = { ...} associates from left to right so that,
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for example,
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a = {e_0, ... } = {v_0, ...}
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first assigns e_0, ... to the elements of a, and then assigns v_0, ...
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to the result.
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If there are side effects in the evaluations involved in executing a = b,
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it should be noted that the order of evaluations is: first the address
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for a, then the value of b, and finally the assignment. For example if
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A is a matrix and i = 0, then the assignment in A[i++] = A[i] is
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that of A[0] = A[1].
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If, in execution of a = b, a is changed by the evaluation of b, the
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value of b may be stored in an unintended or inaccessible location. For
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example,
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mat A[2]= {1,2};
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A[0] = (A = 3);
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results in the value 3 being stored not only as the new value for A
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but also at the now unnamed location earlier used for A[0].
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EXAMPLE
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; b = 3+1
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; a = b
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; print a, b
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4 4
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; obj point {x,y}
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; mat A[3] = {1, list(2,3), obj point = {4,5}}
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; A[1][[0]] = 6; A[2].x = 7
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; print A[1]
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list (2 elements, 2 nonzero):
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[[0]] = 6
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[[1]] = 3
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; print A[2]
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obj point {7, 5}
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; A = {A[2], , {9,10}}
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; print A[0]
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obj point {7, 5}
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; print A[2]
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obj point {9, 10}
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; A = {, {2}}
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print A[1]
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list (2 elements, 2 nonzero):
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[[0]] = 2
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[[1]] = 3
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LIMITS
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none
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LINK LIBRARY
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none
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SEE ALSO
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swap, quomod
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## Copyright (C) 1999 Landon Curt Noll
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##
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## Calc is open software; you can redistribute it and/or modify it under
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## the terms of the version 2.1 of the GNU Lesser General Public License
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## as published by the Free Software Foundation.
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##
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## Calc is distributed in the hope that it will be useful, but WITHOUT
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## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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## or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General
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## Public License for more details.
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##
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## A copy of version 2.1 of the GNU Lesser General Public License is
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## distributed with calc under the filename COPYING-LGPL. You should have
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## received a copy with calc; if not, write to Free Software Foundation, Inc.
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## 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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##
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## Under source code control: 1995/05/11 21:03:23
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## File existed as early as: 1995
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##
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## chongo <was here> /\oo/\ http://www.isthe.com/chongo/
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## Share and enjoy! :-) http://www.isthe.com/chongo/tech/comp/calc/
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