sin function strange problem
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I have a strange problem that I do not understand. If I use sin(p1) inside a program and in command window, both gave different result.
case-1
% code
A=dlmread('data.dat',',',[1 0 639*60 22]);
p1=A(1,6)
whos p1
p1=2*pi*70e6*p1
whos p1
p2=sin(p1)
whos p2
end
when I run it in command window all p1, p2 shows double and result shows is
p1 = 3.0058e+008 p2 = 2.0422e-008
but in command window if i enter p1 as 3.0058e+008 then sin(p1) = -0.9611
why this difference. pls help
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Jan
2012년 11월 28일
편집: Jan
2012년 11월 28일
The command format controls the precision of the output. Try this to show more digits of the values:
p1 = 3.0058e+008
p2 = p1 + 1
format long g
p1
p2
format short g
p1
p2
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추가 답변 (1개)
Ilham Hardy
2012년 11월 28일
Perhaps you don't use the same value of p1..
HINT:
sin(95000)
ans =
-0.9818
sin(9.5e4)
ans =
-0.9818
sin(95454)
ans =
-0.1506
sin(95545)
ans =
0.2545
댓글 수: 7
Jan
2012년 11월 28일
편집: Jan
2012년 11월 28일
Are you really sure, that "p1" in your function is exactly 3.0058000000000000e8 and if so, how did you test it? Please note that tiny rounding errors must occur when the binary value is converted to decimal for the display. There are e.g. a lot of sin waves between 3.005800e8 and 3.005799e8, but with 5 digits precision both values are displayed equally.
I'm still convinced that the number inside the function is displayed with 5 digits only and that the following digits are not zero. Therefore I still think that "format long g" allows to see this difference, although it cannot "solve" it. But there is no way to "solve" it, because it is based on a misunderstanding only.
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