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Numerical calculation error using eval

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Mike
Mike 2012-3-6
关闭： MATLAB Answer Bot 2021-8-20
I'm going through a calculation to convert RH to dewpoint, and for the first step I need to get the saturation vapor pressure, es.
es=eval(['6.11*exp(((Lv*Mw)/R)*((1/273)-(1./temp_ruc_',eventlist(z,:),')));']);
The error occurs within the exponent term...
I evaluated (Lv*Mw/R) and ((1/273)-(1./temp_ruc_',eventlist(z,:),')) separately, and both work.
I also tried the whole term using a sample temperature value (290 K), and I got the right answer:
((Lv*Mw)/R)*((1/273)-(1/290)) = 1.1632e+03
Given the range of temp values, all the answers should be in this range... But when I go through the calculation in full, as shown below, I get values ranging from -6 to +2...
eval(['((Lv*Mw)/R)*((1/273)-(1./temp_ruc_',eventlist(z,:),'))'])
What could be causing this error?
  1 个评论
Jan
Jan 2012-3-7
Avoid EVAL. It provokes errors and problems - obviously. And there is always a better solution.

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Walter Roberson
Walter Roberson 2012-3-6

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