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T O P I C R E V I E W
biotecDD	Posted - 05/28/2004 : 10:23:48 AM Dear sirs, I need to fit my data with the following function: (1-erf(sqrt(1+x)))*exp(1+x)/sqrt(1+x) According to the analysis, this should be a continuous positive decreasing function of positive argument. However, for arguments x<~30, Origin computes reasonable values, whereas for x>30 the values computed are exactly 0. Obviously, this is related to the limited precision of computer arithmetic. In principle it is possible to approximate this funtion for x>~10 by an asymptotic series, which will not converge well for small x (say, for x~1). Is it possible to combine in one fitting function the analytical expression for x<10 and series expansion for x>10? Or could you please suggest another solution for this problem?
1 L A T E S T R E P L I E S (Newest First)
easwar	Posted - 05/28/2004 : 10:40:21 AM quote: Is it possible to combine in one fitting function the analytical expression for x<10 and series expansion for x>10? Or could you please suggest another solution for this problem? Hi, You can certainly define the fitting function to be different above and below a certain x, such as: if ( x < 10 ) y = <expression1>; else y = <expression2>; This appears to be the only way since erf() converges to 1 at low x. Easwar OriginLab Edited by - easwar on 05/28/2004 10:41:41 AM

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