Undefined function 'abs' for input arguments of type 'function_handle'

2017 11 9
1 个回答
更新时间：2017 11 15
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0 个投票

function [root,rootHistory, iter,errorValue]=myNewton(fh,dfh,initialGuess, tol , maxIter )
numLoop = 0;
rootHistory = [];
x = initialGuess;
a = @(x)fh;
while abs(a) >= tol
x1 = initialGuess - fh/dfh;
initialGuess = x1;
numLoop = numLoop + 1;
rootHistory = [rootHistory x1];
if numLoop == maxIter
break
end
end
root = x1;
iter = numLoop;
errorValue = abs(fh(root));
end
I don't know why it is giving me this error statement. There are also other syntax error in my code as well. Can someone help please? The instructions are in the PDF

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bdlawr
bdlawr 2017-11-9
when i take out the "abs" it gives me this ==>
Undefined operator '>=' for input arguments of type 'function_handle'.
perhaps there is something wrong with my function handle? Sorry new to matlab...

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回答（1 个）

Walter Roberson
Walter Roberson 2017-11-9

0 个投票

You need to change
a = @(x)fh;
to
a = fh(x);
You need to change
to
x1 = initialGuess - fh(SOMEINPUT)/dfh(SOMEINPUT);
You will need to figure out what is appropriate for SOMEINPUT.
You will also need to change a somewhere in the loop.

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bdlawr
bdlawr 2017-11-9
编辑：bdlawr 2017-11-9
wait fh is function that i define as x^3 + 2x^2 - 10x. i need to plug in initialGuess into fh to test whether the while loop condition is true. thats why i used an anonymous fcn or am i using it incorrectly. there should be an image of the instruction under 'latest activity'. thank you so much for helping me
Walter Roberson
Walter Roberson 2017-11-9
No, fh is a handle to a function. It says so right in your instructions.
To invoke a function handle, you name the function handle, then ( then the list of parameters then ) -- just like the fh(x) that I showed.
bdlawr
bdlawr 2017-11-9
it now says
"Index exceeds matrix dimensions.
Error in myNewton (line 5) a = fh(x);"
but the autograder does give me 4 extra points
bdlawr
bdlawr 2017-11-9
编辑：Walter Roberson 2017-11-15
function [root,rootHistory, iter,errorValue]=myNewton(fh,dfh,initialGuess, tol , maxIter )
numLoop = 0;
rootHistory = [];
x = initialGuess;
a = fh(x);
while a >= tol
x1 = initialGuess - fh(x)/dfh(x);
initialGuess = x1;
numLoop = numLoop + 1;
rootHistory = [rootHistory x1];
if numLoop == maxIter
break
end
end
root = x1;
iter = numLoop;
errorValue = abs(fh(root));
end
Walter Roberson
Walter Roberson 2017-11-15
In the first position, are you passing in
x.^3 + 2*x.^2 - 10*x
or are you passing in
@(x) x.^3 + 2*x.^2 - 10*x
?

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