Suppressing tiny imaginary parts in complex numbers

Question

How do I extract the real part of a substitution expression from FindRoot or Solve? Or alternately, how do I insist that they return real results?

For example, FindRoot returns something of the form:

{x->A + B I}

Analytically, I know that x must be real. Because B is 17+ orders of magnitude smaller than A, I assume it's numerical slop.

If I do:

Re[FindRoot[expr, {x, guess}]]

it simply returns:

Re[{x->A + B I}]

Assumptions aren't helping:

Assuming[Element[x, Reals], FindRoot[expr, {x, guess}]] ]

still returns x with a small imaginary component. Any suggestions?

This is surely a duplicate. Could we please close it as such rather than "easily found in the documentation?" — Mr.Wizard, Apr 14 '15 at 18:58
Related: (5235), (17809), (52353), (60278) - The last one seems the closest duplicate, but I'm surprised there isn't an older one. — Michael E2, Apr 14 '15 at 19:41
I did search before asking, but couldn't find anything after a few tries. Chop works, but I wouldn't say it's easy to find in the documentation unless you already know it's there... — Paul T., Apr 15 '15 at 21:21

score 5 · Accepted Answer · answered Apr 14 '15 at 17:08

5

Chop[FindRoot[expr, {x, guess}]]

answered Apr 14 '15 at 17:08

Ivan

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Suppressing tiny imaginary parts in complex numbers

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