ArcCosine function
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Zelda Luxenburry
el 6 de Feb. de 2012
Comentada: John D'Errico
el 13 de En. de 2021
this is the code i have so far. i need to write a function m-file that can solve the arc cosine function for [0, 2pi]. it is giving me an error when i try acosfull(0,0), it does not give me the error....what am i missing?
function [theta] = acosfull(x,y)
%acossfull: find output angle of arccos over 0<theta<2*pi
% find value of acos(z) in the correct quadrant over the full range [0
% 2pi]
if y==x==0
theta=0
disp('Error.')
else r=sqrt(x^2 + y^2);
z=x/r;
acos(z)
end
2 comentarios
Walter Roberson
el 29 de Oct. de 2020
Not at all. MATLAB does not have any implicit multiplication, not anywhere, so there is no danger that acos(z) might be interpreted as a*cos(z)
Respuesta aceptada
Walter Roberson
el 6 de Feb. de 2012
y==x==0
is parsed as
((y==x)==0)
So it compares x to y to give 0 (false) or 1 (true), and then it compares that 0 or 1 to 0. Effectively what you coded is
if y ~= x
Try
if y == x && y == 0
Más respuestas (2)
Wolfgang Garn
el 8 de Ag. de 2013
Editada: Wolfgang Garn
el 8 de Ag. de 2013
In short theta = acos(x./sqrt(x.*x+y.*y)) + (y<0)*pi or below with a couple of tests.
function theta = acosfull(x,y)
%acossfull: find output angle of arccos over 0<theta<2*pi
% find value of acos(z) in the correct quadrant over the full range [0 2pi];
% acosfull requires as input x and y coordinates (length of x and y side of a rectangular triangle).
if nargin<1 % then give examples
disp('A series of examples:');
disp('45° = acosfull(2,2) radians: '); acosfull(2,2)
disp('90° = acosfull(0,3) radians: '); acosfull(0,3)
disp('135° = acosfull(-2,2) radians: '); acosfull(-2,2)
disp('180° = acosfull(-2,0) radians: '); acosfull(-2,0)
disp('225° = acosfull(-3,-3) radians: '); acosfull(-3,-3)
disp('270° = acosfull(0,-4) radians: '); acosfull(0,-4)
disp('315° = acosfull(2,-2) radians: '); acosfull(2,-2)
disp('360° = acosfull(2,-0.001) radians: '); acosfull(2,-0.001)
disp('NaN = acosfull(0,0): '); acosfull(0,0)
acosfull([2 -2 -2 -2 0], [2 2 -2 -2 0])
end
if nargin<2 % then display warning (and attempt original acos)
warning('acosfull requires as input x and y coordinates (or length of x and y side of a rectangular triangle).');
if nargin>0, theta = acos(x); end
else
theta = acos(x./sqrt(x.*x+y.*y)) + (y<0)*pi;
end
3 comentarios
Steven Lord
el 13 de En. de 2021
Can you show us the code you ran and describe specifically what about the answers didn't work?
- Do you receive warning and/or error messages? If so the full and exact text of those messages (all the text displayed in orange and/or red in the Command Window) may be useful in determining what's going on and how to avoid the warning and/or error.
- Does it do something different than what you expected? If so, what did it do and what did you expect it to do?
- Did MATLAB crash? If so please send the crash log file (with a description of what you were running or doing in MATLAB when the crash occured) to Technical Support using the telephone icon in the upper-right corner of this page so we can investigate.
Danay Rosh
el 7 de Abr. de 2019
arccos(pi/2)
4 comentarios
John D'Errico
el 13 de En. de 2021
I might also add that the number acos(pi/2) will not even be a real number, but imaginary.
acos(pi/2)
ans =
0 + 1.0232i
The set of inputs for which acos will produce REAL results is limited to the interval [-1,1].
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