[Maxima-bugs] [ maxima-Bugs-2051391 ] subst command does not work with equation list

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Bugs item #2051391, was opened at 2008-08-14 06:37
Message generated for change (Comment added) made by robert_dodier
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Category: Lisp Core - Simplification
Group: None
>Status: Closed
>Resolution: Wont Fix
Priority: 5
Private: No
Submitted By: Dr. Schorsch (xorx)
Assigned to: Nobody/Anonymous (nobody)
Summary: subst command does not work with equation list

Initial Comment:
The subst command does not work the same way with a list of substitution equations as with a directly specified substitution.

Example:
(%i1) h:sin( y + 2*x)*cos(y+2*x)-(y+2*x)*3;
(%o1) cos(y+2*x)*sin(y+2*x)-3*(y+2*x)(%i2) 

(%i2) subst(a,y+2*x,h);
(%o2) cos(a)*sin(a)-3*a(%i3)

(%i3) subs:[a=y+2*x];
(%o3) [a=y+2*x]

(%i4) subst(subs,h);
(%o4) cos(y+2*x)*sin(y+2*x)-3*(y+2*x)

(%i5) subst([a=y+2*x],h);
(%o5) cos(y+2*x)*sin(y+2*x)-3*(y+2*x)

Expression 2 does work fine, while expression 3,5 and 5 do not produce the expected result.

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>Comment By: Robert Dodier (robert_dodier)
Date: 2008-08-14 18:02

Message:
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user_id=501686
Originator: NO

I think subst([y + 2*x = a], h) works as expected (i.e. with the equation
turned around).

When the subst argument is a list of equations, the left-hand side of each
equation is the term to be replaced --- that is different from the form
subst(foo, bar, baz) in which bar is to be replaced. Sorry that this is
confusing.

Closing this report as "won't fix" since it is only a case of confusion,
and I don't think it is serious enough to warrant changing subst.

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