|Re: 42s questions and 42s vs 35s|
Message #8 Posted by Dieter on 18 Sept 2011, 8:08 a.m.,
in response to message #1 by snaggs
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Programs for the Gaussian CDF and its inverse (quantile) are a very weak point in HP software. The one or other program even may be used as an example for errors and pitfalls that have to be avoided in numeric software. Most even resort to the good old Hastings approximation from the Fifties which is only good for three decimals.
1. Cant seem to find a Normal distribution program for the 42s?
Of course you can do both the CDF and the quantile using the 42s' Integrate and Solve, but there are far better options here. Some of them have been discussed for the 34s project.
What precision do you need? And what range of z resp. p has to be covered?
Since there is no equation mode on the 42s you will have to use RPN. While speed may be comparable in general terms, there is something the 42s cannot do: solving your equation symbolically. The 35s (in most cases) can do that if (!) the variable to solve for appears only once. A very simple example for the Pythagorean theorem on the 35s:
2. Once I get my head around it, will I be able to do the equivalent of the equation solver on the 35s on the 42s?
A^2 + B^2 = C^2
You now can solve for any variable and the 35s will return the result immediately. No inital guesses required, no iteration, no nothing. Press SOLVE A. You are prompted for B and C, and the value for A is returned within a fraction of a second. In fact, the 35s rearranges the equation and evaluates A as the square root of C^2 - B^2.
Or, try the example in the 15C manual, a stone dropped from the Eiffel tower: h = g/2 t2
H = g / 2 * T^2
Yes, the 35s also knows the value for g. ;-)
Solve T, enter H and get the result instantly. Replace the constant g by a variable G and you can also solve for that. I really like that. ;-)
I assume both use the same or at least very similar algorithms, so there should not be much difference. The nice thing on the 35s however is that you can also solve and integrate equations.
Is the accuracy on solve and integration as good as 35s
There may be a difference if the 35s uses the mentioned feature and solves an equation symbolically. Consider X^2 = 8. The iterative approach on the 42s should return two adjacent results 2,82842712475 and ...474 (the exact value is somewhere in between), while the 35s evaluates X = SQRT(8) and returs only that result (...475).
This example also shows that you will always get one single result, so in this case the negative root will not be returned. In theses cases it's easy to force an iterative calculation: simply add 0*X to the equation so that X appears twice. ;-)
There are several things on the 42s that are awesome. ;-) However, it does not offer any kind of mass storage or communication with something other than a printer. A 42s with a 41C-style keyboard (and alpha entry) with a simple SD(HC/XC) slot - that would be something that made (not only) my dreams come true.
The menu system and polish on the 42s is awesome