Clear Filters
Clear Filters

Trying to answer a math problem using newton's method but having problem in the function.

2 views (last 30 days)
This is the last function when newton's method is applied:
I used z=log(x) in my function to make it easier to understand:
clc
x=0.25;
y=0;
while (y-x)<10^-4
z=log10(x);
y = x-((((x ^ 2)z-(x ^ 0.5)-20)2.x ^0.5)/(-1+4.x ^ (3/2)z+2.x ^ (3/2)))
Invalid expression. Check for missing multiplication operator, missing or unbalanced delimiters, or other syntax error. To construct matrices, use brackets instead of parentheses.
x=y;
end

Accepted Answer

Alan Stevens
Alan Stevens on 17 Mar 2023
Matlab doesn't like implied multiplication
(x ^ 2)z
should be
(x ^ 2)*z
etc.
Also, in Matlab
log(x)
is ln(x)

More Answers (2)

Cris LaPierre
Cris LaPierre on 17 Mar 2023
You need to include the multiplication operator when coding your equation. Also, it is '*', not '.'. Nothing is inferred.
I think your conditional will be problematic, since the last line of your loop sets x equal to y.
x=0.25;
y=0;
while (y-x)<10^-4
z=log10(x);
y = x-((((x ^ 2)*z-(x ^ 0.5)-20)*2*x ^0.5)/(-1+4*x ^ (3/2)*z+2*x ^ (3/2)))
x=y;
end
  1 Comment
Cris LaPierre
Cris LaPierre on 17 Mar 2023
Edited: Cris LaPierre on 17 Mar 2023
+1 about log10 vs log for natural ln.
Also wanted to point out that you have created an infinite loop. Since x=y, (y-x) is 0, which is <1e-4. Since your condition will always be true, your loop will never end.
Just changing the < to > will prevent the infinite loop, but won't fix the issue that y=x. Consider creating a third variable to prevent this.
Also consider the case that the difference of (y-x) may be positive or negative. You may want your condition to compare to the absolute value of this difference.

Sign in to comment.


Voss
Voss on 17 Mar 2023
Multiplication is * or .* but never . as in 4.x and never implicit as in (x^2)z
log10 is base-10 logarithm. log is natural logarithm.
z = log(x);
y = x-((((x^2)*z-(x^0.5)-20)*2*x^0.5)/(-1+4*x^(3/2)*z+2*x^(3/2)));

Categories

Find more on Mathematics in Help Center and File Exchange

Products


Release

R2022b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!