CODEWITHSUNDEEP
matlabwolfram-mathematica
user9727931
user9727931

Reputation: 11

Translate Matlab to Mathematica, fixed-point iteration

This is my Matlab code:

clear;clc;format ('long','g')
i=1;
x(i)=0;
error(i) = 9999;

while error(i) >= 0.05
    x(i+1) = (0.2062129)*(20+(2*x(i)))^(2/5);
    error(i+1)=abs((((x(i+1)-x(i))/(x(i+1)))*100));
    i=i+1;
end

disp('           root                 error(%)');
disp([x',error'])

How do I translate this into Mathematica so that it generates the list of roots and errors the way it does in matlab?

Upvotes: 0

Views: 111

Answers (2)

agentp
agentp

Reputation: 6989

I'd suggest instead of burying the convergence test in the function you do like this:

f[xi_] := 0.2062129*(20 + (2*xi))^(2/5)
NestWhileList[f, 0, Abs[(#2 - #1)/#2*100] >= .05 &, 2]

{0, 0.683483, 0.701799, 0.70228, 0.702293}

You can also do:

FixedPointList[f, 0, SameTest -> (Abs[(#2 - #1)/#2*100] < .05 &)]

Note in both cases you can use FixedPoint and NestWhile if you just want the final result , not the list of intermediate values.

Upvotes: 0

Bill
Bill

Reputation: 3957

Since we don't have the output you got from Matlab it is difficult to know whether this is correct enough or not. Compare it to what you have and go from there.

expr={1,0,9999};
f[{i_,xi_,err_}]:=(xipp=0.2062129*(20+(2*xi))^(2/5);
  {i+1,xipp,Abs[(((xipp-xi)/(xipp))*100)]});
NestWhileList[f,expr,#[[3]]>=.05&]

which in a fraction of a second returns

{{1,0,9999},
 {2,0.683483,100.},
 {3,0.701799,2.60989},
 {4,0.70228,0.0684954},
 {5,0.702293,0.00179788}}

Upvotes: 1

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