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ClearAll
(*befor finding the root for a lower stiffness use NSlove to find , \
then put that value back on the Rootfind and find the beta for \
varying stiffness *)
Y = 2*10^11;
Iyy = 8.333*10^-6;
L = 4;
z = Array[# &, 50, {0.01, 0.5}];
T = Length[z];
k = 10^12;(*1*10^b;*)
a = 1/(4*b^3*(1 - Cosh[b]*Cos[b]));
phi1 = ConstantArray[0, {T, 1}];
phi2 = ConstantArray[0, {T, 1}];
phi3 = ConstantArray[0, {T, 1}];
phi4 = ConstantArray[0, {T, 1}];
eq = ConstantArray[0, {T, 1}];
eq1 = ConstantArray[0, {T, 1}];
S = ConstantArray[0, {T, 1}];
om = ConstantArray[0, {T, 1}];
fn = ConstantArray[0, {T, 1}];
a1 = (Cos[b*x] - Cosh[b*x]);
a2 = (Sin[b*x] - Sinh[b*x]);
For[i = 2, i < T + 1, i++,
  phi1[[i]] = (Cos[b] - Cosh[b])*(Sin[b*(1 - z[[i]])] - 
      Sinh[b*(1 - z[[i]])]);
  phi2[[i]] = (Sin[b] - Sinh[b])*(Cos[b*(1 - z[[i]])] - 
      Cosh[b*(1 - z[[i]])]);
  phi3[[i]] = (Sin[b] + Sinh[b])*(Sin[b*(1 - z[[i]])] - 
      Sinh[b*(1 - z[[i]])]);
  phi4[[i]] = (Cos[b] - Cosh[b])*(Cos[b*(1 - z[[i]])] - 
      Cosh[b*(1 - z[[i]])]);
  eq[[i]] = 
   a ((phi1[[i]] - phi2[[i]])*(a1 /. x -> z[[i]]) + (phi3[[i]] + 
         phi4[[i]])*(a2 /. x -> z[[i]])); eq1[[i]] = 1 + (k*eq[[i]])];
f[x_] := eq1[[2]] /. b -> x;
p = Plot[f[x], {x, 0, 30}, Mesh -> {{0}}, MeshFunctions -> (f[#] &)]
seeds = Cases[Normal[p], Point[r_] : -> r[[1]], \[Infinity]]
roots = Tabel[
   x /. FindRoot[f[x], {x, s}], {s, 
    seeds}] \[Union] (SameTest -> (Abs[#1 - #2] < 1/10^-6 &))

tried to extract the first four roots (all the roots at a time ) of the transcendental equation but not working. It is throwing some error. find root, nsolve, find roots with the interval is also not working.

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    $\begingroup$ How about if you show the first place you get an error, provide code to duplicate that error, and tell us what the error is. "Not working" is not a very descriptive. $\endgroup$
    – bill s
    Nov 22, 2017 at 18:59
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    $\begingroup$ In the definition of seeds replace : -> with :> In the definition of roots. you misspelled Table. In the SameTest change 1/10^-6 (i.e., 10^6) with 10^-6 $\endgroup$
    – Bob Hanlon
    Nov 22, 2017 at 19:04
  • $\begingroup$ @BobHanlon [best answer] . thanks, problem solved. apparently, i did some typo i code . could you suggest me best coding practice? $\endgroup$ Nov 23, 2017 at 7:07

1 Answer 1

1
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You can use GraphicsMeshFindIntersections. Although this depends on the sampling (PlotPoints) of the plot (and your required accuracy):

p = Plot[{f[x], 0.}, {x, 0.1, 30}, PlotPoints -> 350];
intersections = Graphics`Mesh`FindIntersections[p] // Chop

Labeled[Show[p, Frame -> True, Axes -> False, 
Epilog -> {PointSize[.025], Red, Point[intersections]}], 
Style[#, 20] &@Column[N[intersections, 10], Frame -> All], Right]

enter image description here

Just bracket your interval to find the solutions you are looking for.

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  • $\begingroup$ Thanks, alot sir. It was really helpful. Best answer $\endgroup$ Nov 24, 2017 at 17:59

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