Help with loop error

2 次查看（过去 30 天）
amateurintraining
amateurintraining 2017-10-13
评论： James Tursa 2017-10-14
My function is as follows but keeps coming up with the error that the output argument "approx" is not assigned. How do I change it to produce the desired outputs?
function [ exact, approx, abs_error, terms ] = calcTaylorTerms( x, dx, tol, max_terms, exp_or_sin )
%CALCTAYLORTERMS
% x: is x
% dx: delta x
% tol: the error tolerance to be met
% max_terms: the maximum number of terms to include before giving up
% exp_or_sin: a flag that determines whether f(x)=e^x or f(x)=sin(x)
% exact: analytical solution to f(x+deltax)
% approx: the Taylor series approximation of f(x+deltax)
% abs_error: the absolute value of the difference between the exact
% solution and the Taylor series approximation
% terms: the number of terms ultimately used in the Taylor series
if isequal(exp_or_sin,"exp")||isequal(exp_or_sin,"sin")
if isequal(exp_or_sin,"exp")
exp_or_sin=exp(x);
elseif isequal(exp_or_sin,"sin")
exp_or_sin=sin(x);
end
abs_error=0;
n=1;
count=0;
terms=1;
while abs_error>=tol && n>1 && terms>max_terms
count=count+1;
terms(count)=exp_or_sin+(1)^(count+1)*(dx^n).*diff(exp_or_sin,x,n)/factorial(n);
approx(count)=sum(terms);
n=n+1;
exact=exp_or_sin(x+dx);
abs_error=abs((exact-approx)/exact);
end
exact=exp_or_sin(x+dx);
approx=approx;
abs_error=abs_error
X=terms;
X(:)=1;
terms=sum(X)
else
exact=NaN;
approx=NaN;
abs_error=NaN;
terms=NaN;
end
end

请先登录，再回答此问题。

回答（1 个）

James Tursa
James Tursa 2017-10-13
编辑：James Tursa 2017-10-13
Maybe move all of the default stuff prior to your if test. E.g.,
exact = NaN;
approx = NaN;
abs_error = NaN;
terms = NaN;
if isequal(exp_or_sin,"exp")||isequal(exp_or_sin,"sin")
:
etc
  2 个评论
amateurintraining
amateurintraining 2017-10-13
Unfortunately, if I do that it just produces approx=NaN, which means that the variable is still not defined. How do I call a variable out of a while-loop?
James Tursa
James Tursa 2017-10-14
If it is coming back as NaN, that gives you a clue. Namely, that these values were not set inside the while loop. Use the debugger to step through your code and figure out why you are not getting inside that while loop.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Configure Simulation Conditions 的更多信息

标签

Community Treasure Hunt

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

Start Hunting!

Translated by