Handling failed FindRoot calls

Question

I want to handle FindRoot calls which did not converge (e.g "thrown" error message FindRoot::cvmit)

sols = Table[FindRoot[some equations dependant in a, startSolutions], 
    {a, minA, maxA, stepSize}]

For some, FindRoot will not converge (3000 iterations). Is there a way to define the entry of sol in this case to e.g. NAN?

EDIT: Is there a possibility to break further evaluation of the Table call, if Check[] returns a defined value?

Break[] is only allowed in For[], While[] and Do[] - so do I have to encapsulate my FindRoot call in an extra loop and construct the table by hand?

e.g.: (** apply solver and Check[] if jacobian gets singular **)

sols = {};

For[Alpha = minAlpha, Alpha <= maxAlpha, Alpha += stepSize, Append[sols, Check[solver, {Alpha, Break[]}, {FindRoot::jsing}]]];

Unfortunately this does not work...

Answer 1

You can use Check to return an alternate result and use Quiet to avoid the messages that you are expecting anyway. Here's an example:

Quiet[Table[Check[x /. FindRoot[x^2 - c, {x, 1}],
  "NaN", {FindRoot::lstol, FindRoot::jsing}], {c, -5, 5}],
  {FindRoot::lstol, FindRoot::jsing}]

One important note is to make sure that the Check is inside the Quiet, and not the other way around. If Quiet is inside Check the message will be "quieted" before it is seen by Check and so you won't get "NaN".