Task: Finding roots in loop

t = List[1, 2, 3, 4, 5]
fx[x_] := a*x^2 - 5
List[Do[Print[FindRoot[fx[k] == 1, {a, 1}]], {k, 0, 5}]]

Output: Currently the output is as follows:

 {a-> 6}
 {a-> 1.5}

and so forth

But I want to have the values of a in a List in order to perfom further tasks (Plotting root of f_a against a)

  • 3
    $\begingroup$ Using Table and Map are things you should get really comfortable with in general, so look them up in documentation center, and browse around here a bit: wolfram.com/support/learn $\endgroup$ – ssch Feb 11 '13 at 16:06
  • 1
    $\begingroup$ Please try to avoid procedural loops $\endgroup$ – Dr. belisarius Feb 11 '13 at 16:31
  • 2
    $\begingroup$ Don't use Print to generate values that you want to process further on. ssch has good advice. The List you use doesn't make sense here either. Another advice: Generally you should not define functions that have more dependencies than shown by the variables in the call pattern. In your case, the function depends on a as well, but that is not made explicit. $\endgroup$ – Sjoerd C. de Vries Feb 11 '13 at 16:48

You have many many options. Here are just two:

Table[FindRoot[fx[k] == 1, {a, 1}], {k, t}]


FindRoot[fx[#] == 1, {a, 1}] & /@ t

Here is one way to make a plot of t vs the roots:

pts = Table[{k, a /. FindRoot[fx[k] == 1, {a, 1}]}, {k, t}];

Example plot of t vs roots

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