How can I get the "zero" value of cosine function in radians??

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Yasir
Yasir 2016-3-11
回答： Steven Lord 2016-3-11
Due to the approximations and radian values used by MATLAB, I can't get "zero" value of cosine function. "acos(0)" gives answer of 1.5708 radians, but Cos(1.5708) doesn't lead to "zero". Can anyone help??
  2 个评论
Roger Stafford
Roger Stafford 2016-3-11
Please show us your actual computations. You are only showing values in 'format short' here which is not very accurate. Expressed to greater accuracy the arc-cosine of zero would for example be 1.570796327
Yasir
Yasir 2016-3-11
clc clear all
v1=1; v2=1; v3=1; s1=0; s2=0; s3=0;
z12=0.08j ; z13=0.04j; z23=0.01j; y12=1/z12; y13=1/z13; y23=1/z23;
Y11=y13+y12 ; Y12= -y12 ; Y13=-y13; Y21= -y12 ; Y22=y12+y23; Y23=-y23; Y31= -y13 ; Y32= -y23 ; Y33=y23+y13;
A=[Y11 Y12 Y13; Y21 Y22 Y23; Y31 Y32 Y33]
O=angle (A) Y=abs (A)
P2=v2*v1*Y(2,1)*cos(O(2,1)-s2+s1)+v2*v2*O(2,2)*cos(O(2,2))+v2*v3*Y(2,3)*cos(O(2,3)-s2+s3)
P2 should give output of zero..

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Steven Lord
Steven Lord 2016-3-11
Use the degree-based trig functions or Symbolic Math Toolbox.
d = acosd(0);
cosd(d)
ds = acos(sym(0));
cos(ds)
There's a brief discussion of this sort of scenario [where cos(pi/2) is close to, but not exactly equal to, 0] in the Cleve's Corner article from February 2002 that you might find informative.

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