How to erase definition introduced by using Set instead of Equal in Solve

Question

When trying to solve a set of equations, I made a mistake by using = instead of ==. Now when I fixed the mistake, the equation still always yield True. Switching the kernel off and back on would solve the problem, but is there a better way?

Sample code:

DSolve[y'[t] = 2, y[t], t]
(*DSolve::deqn: Equation or list of equations expected instead of 2
in the first argument 2*)

DSolve[y'[t] == 2, y[t], t]
(*DSolve[True, y[t], t]*)

maybe you might try something like Remove[y] or Remove["Global`"]? — Harry, Mar 01 '16 at 14:20
@MikeLimaOscar : You could have written your answer as an Answer... — Eric Towers, Mar 01 '16 at 14:40
@EricTowers Yes, could have but I think it is a candidate for "easily found in the docs" closure. — MikeLimaOscar, Mar 01 '16 at 15:16
@MikeLimaOscar Could you explain why Clear[y] doesn't work? Thanks! — arax, Mar 02 '16 at 07:14
Clear[y] doesn't work because your mistaken definition is not associated with the symbol y. It is a SubValue of Derivative which is the Head of the FullForm of the expression. See this question for the answer to your probable next question! — MikeLimaOscar, Mar 02 '16 at 11:41

score 3 · Accepted Answer · answered Mar 01 '16 at 14:48

From the docs:

Unset (=.)

lhs=.

removes any rules defined for lhs.

Rules are removed only when their left-hand sides are identical to lhs, up to renaming of patterns.

Undefine a value:

In[1]:= x = 5;

In[2]:= x =.

In[3]:= x

Out[3]= x

How to erase definition introduced by using Set instead of Equal in Solve

1 Answers1