Azzera filtri
Azzera filtri

Wrong result from calculation

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Veselin Manev
Veselin Manev il 9 Giu 2020
Commentato: Veselin Manev il 9 Giu 2020
Dear all,
I have a question about high precision calculation of the fraction 1/998001 in Matlab. I use
vpa(1/998001,200)
which produces the following result
0.000001002003004005005955287066314596255978131011943332850933074951171875
On the Numberphile channel on youtube, they prove that the result should be
0.000001002003004005006007 .. 996997999
which has higher precision than the obtain result in MATLAB and it appears that there is some numerical error. Do you have any idea why is that?
Thank you
Regards,
Veselin

Risposte (1)

Steven Lord
Steven Lord il 9 Giu 2020
By the time you call vpa, MATLAB has already performed the division in double precision. So you're displaying the double precision value that results from that division to 200 decimal places.
Perform the division symbolically.
x1 = vpa(1/998001, 200)
x2 = vpa(sym(1)/998001, 200)
  2 Commenti
madhan ravi
madhan ravi il 9 Giu 2020
“Power of symbolic toolbox” never lets down ;)
Veselin Manev
Veselin Manev il 9 Giu 2020
Thank you very much!

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