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Undefined function 'equation' for input arguments of type 'double'

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xtz xtz
xtz xtz on 8 Apr 2020
Edited: per isakson on 9 Apr 2020
I want to write a function equation(M,epsilon,tol) which sets the solution of with an approximation error . So I have:
function x=newtonp(f, x, tol, h)
if nargin<4
h=1e-8
end
if nargin<3
tol=1e-8
end
while abs(f(x))>tol
g=(f(x+h)-f(x))/h
x=x-f(x)/g
end
end
function y=equation(M,epsilon,tol)
y=M+epsilon*sin(x)-x
end
Then I write:
newtonp(@equation(x),x, tol, h)
However I get
Undefined function 'equation' for input arguments of type 'double'
Can anyone correct my code?

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per isakson
per isakson on 8 Apr 2020
foo = @(M,epsilon,x) M+epsilon*sin(x)-x;
foo(0,0,0)
ans =
0
foo(0,1e-6,pi/100)
ans =
-0.031416
I suppose the task is to write one function called equation, which takes three inputs and returns one output.
per isakson
per isakson on 8 Apr 2020
Is this the first time you use Grader?
Why did you write the function called newtonp ?
xtz xtz
xtz xtz on 8 Apr 2020
Yes, it is my first task in Grader. I wrote newtonp because in this task I can't just calculate this equation. My task is to use modified Newton's method to find a sufficient approximation of this function. Therefore, the equation function depends on tol not on x

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Answers (1)

per isakson
per isakson on 8 Apr 2020
Edited: per isakson on 8 Apr 2020
This is my guess
function x = equation( M, epsilon, tol )
h = 1e-8;
x = pi/6; % first guess
foo = @(x) M+epsilon*sin(x)-x;
while abs(foo(x))>tol
g=(foo(x+h)-foo(x))/h;
x=x-foo(x)/g;
end
end
Try it
y = equation(0.5,0.5,1e-8)
y =
0.88786
And why the second input is called epsilon is a mystery to me!

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per isakson
per isakson on 8 Apr 2020
No, isn't "accuracy megatest" mentioned in the task description? Does the test code give any hint?
xtz xtz
xtz xtz on 8 Apr 2020
No, I have oppurtunity to see only pretest test and I have already shown it:
% Run learner solution;
tol = 1e-5;
y = equation(0.5,0.5,tol);
% Run reference solution.
yref = reference.equation(0.5,0.5,tol);
% Compare.
assessVariableEqual('y',yref,'AbsoluteTolerance',2*tol);
Meanwhile, I don't know anything about accuracy megatest.
As for the content of the task, it is its full form:
Write a function x=equation(M,epsilon,tol) which sets the solution of for some with an approximation error such that where a is an exact solution.
per isakson
per isakson on 9 Apr 2020
What's the meaning of "Variable count has an incorrect value." ? Could it refer to the number of variables in the function? No!
Speculation:
  1. Modify the sentence to "The variable, count, has an incorrect value." (It's not your English teacher who wrote that sentence.)
  2. There is a variable named count in the program that evaluates the submission
  3. count is used to keep track of the number of iterations
  4. implementations of numerical methods shall be efficient (among other requirements)
  5. "our" function, equation, might fail an efficiency test. Too many iterations. How did you chose the step value?
  6. Furthermore, in each iteration the function, foo, is evaluated three times for the same value of x. Maybe, count is the number of evaluations of foo().
Your turn!

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