jlg@cochiti.lanl.gov (Jim Giles) (04/25/91)
mjo@ttardis.UUCP (Mike O'Connor) writes: > Well... on an HP-11 or 15, you can take the cosine of pi/2 and get > a number that is not zero. It's rather annoying. In 'radians' mode: The calculator is just being honest. There is no representable number which is exactly equal to pi/2. This means that there is no representable number for which the cosine is exactly zero. This is one of the first tests I make of a calculator: if it gives zero for cosine of _anything_ that can be represented, it probably has a bad cosine function. On the other hand, if your calculator has a 'degrees' mode for the trig functions, you _should_ get zero for the cosine of 90.0 degrees. Similarly for 'grads' mode. J. Giles
henry@zoo.toronto.edu (Henry Spencer) (04/27/91)
In article <22614@lanl.gov> jlg@cochiti.lanl.gov (Jim Giles) writes: >This is one of the first tests I make of a calculator: if it gives >zero for cosine of _anything_ that can be represented, it probably >has a bad cosine function. Well, the HP-48 will give you zero for the cosine of pi/2, but that's because it represents it as "pi/2", not 1.5707... -- And the bean-counter replied, | Henry Spencer @ U of Toronto Zoology "beans are more important". | henry@zoo.toronto.edu utzoo!henry
mjo@ttardis.UUCP (Mike O'Connor) (04/27/91)
In article <22614@lanl.gov>, jlg@cochiti.lanl.gov (Jim Giles) writes: >In 'radians' mode: >The calculator is just being honest. There is no representable >number which is exactly equal to pi/2. This means that there is >no representable number for which the cosine is exactly zero. >This is one of the first tests I make of a calculator: if it gives >zero for cosine of _anything_ that can be represented, it probably >has a bad cosine function. What other calculators have you found this "honesty" on, out of curiosity? Most of the cheapo scientific calculators I have will output 0 for cos of pi/2. I wouldn't necessarily see this as a big problem... depends on the kind of accuracy expected of you. ...Mike Phone: TTARDIS Public Access Unix -- (313) 350-2585 Internet: mjo%ttardis@uunet.uu.net UUCP ("domain"): mjo@ttardis.UUCP UUCP (bang): ...!uunet!sharkey!cfctech!ttardis!mjo