numerical answer required for sumation

조회 수: 38(최근 30일)
john birt
john birt 2011년 3월 2일
a very basic question, say i use
symsum(((-1)^(sym('k')-1))*(sin(sym('k'))), k, 0, 12)
I just get
sin(311/250) - sin(311/125) - sin(311/625) - sin(622/625) - sin(933/625) + sin(311/1250) - sin(1244/625) + sin(933/1250) - sin(1866/625) + sin(2177/1250) + sin(2799/1250) + sin(3421/1250)
but i want a single numeric value (like 0.2354 or whatever) not this expanded string of sin's. I dont want like 0.254 +0.056 +0.214 etc I just want a single value.
Ive tried searching on google but i have the normal problem of not knowing what the keyword is to search for.

채택된 답변

Walter Roberson
Walter Roberson 2011년 3월 2일
You can apply double() to a symbolic expression to get back the Matlab double precision number that is equivalent.
If you want the result to be a symbolic number instead, such as if you need to evaluate to more decimal places, then use vpa() on the symbolic expression.

추가 답변(2개)

Paulo Silva
Paulo Silva 2011년 3월 2일
double(sin(311/250)-sin(311/125)-sin(311/625)-sin(622/625)-sin(933/625)+sin(311/1250)-sin(1244/625)+sin(933/1250)-sin(1866/625)+sin(2177/1250)+sin(2799/1250)+sin(3421/1250))

Paulo Silva
Paulo Silva 2011년 3월 2일
eval('sin(311/250)-sin(311/125)-sin(311/625)-sin(622/625)-sin(933/625)+sin(311/1250)-sin(1244/625)+sin(933/1250)-sin(1866/625)+sin(2177/1250)+sin(2799/1250)+sin(3421/1250)')
  댓글 수: 1
Sean de Wolski
Sean de Wolski 2011년 3월 2일
No reason for eval

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