define a formula - Printable Version +- HP Forums (https://www.hpmuseum.org/forum) +-- Forum: HP Calculators (and very old HP Computers) (/forum-3.html) +--- Forum: HP Prime (/forum-5.html) +--- Thread: define a formula (/thread-874.html) define a formula - fefer92 - 03-09-2014 10:44 PM Hi, I have hp prime and I would like to define a formula to make my calculus easy and faster,the formula is annexed here,anybody can help me please? Thanks RE: define a formula - Stefan - 03-09-2014 11:40 PM Unless you absolutely want to write a function for that (for learning purposes maybe) you don't have to: 1. You could use the mean(L,p) function where L is the list of values and p the list of probabilities. 2. Or if you write L and p as vectors you could just calculate the dot product of the vectors L and p: [L1, L2, L3,...]*[p1, p2, p3...] If p1, p2, etc are not probabilities in range 0 to 1, but frequencies instead (e.g. 3 times, 7 times etc) for method 2 you should also divide by sum(p): E(X)=L*p/sum(p) RE: define a formula - fefer92 - 03-09-2014 11:56 PM (03-09-2014 11:40 PM)Stefan Wrote:  Unless you absolutely want to write a function for that (for learning purposes maybe) you don't have to: 1. You could use the mean(L,p) function where L is the list of values and p the list of probabilities. 2. Or if you write L and p as vectors you could just calculate the dot product of the vectors L and p: [L1, L2, L3,...]*[p1, p2, p3...] If p1, p2, etc are not probabilities in range 0 to 1, but frequencies instead (e.g. 3 times, 7 times etc) for method 2 you should also divide by sum(p): E(X)=L*p/sum(p) Thank you,that really help a little,but I have many formulas similar to this one,like this formula annexed below and I would like to know how to make this one to ... RE: define a formula - Stefan - 03-10-2014 12:10 AM lol, expectancy, entropy... looks like your studying for the same exam than I do :-D Here you can again use the dotproduct and make use of the fact that you can apply most of the functions to lists and vectors. log_2(p) applies log_2 to the vector p (the log_n(x) template is in the math templates). And then just multiply p and log_2(p), just as before: H(x)=p*log_2(p) P.S: You can type equations in this forum in Latex syntax if you surround them with two $in the front and back: $$\frac{1}{x}$$ RE: define a formula - fefer92 - 03-10-2014 01:05 AM (03-10-2014 12:10 AM)Stefan Wrote: lol, expectancy, entropy... looks like your studying for the same exam than I do :-D Here you can again use the dotproduct and make use of the fact that you can apply most of the functions to lists and vectors. log_2(p) applies log_2 to the vector p (the log_n(x) template is in the math templates). And then just multiply p and log_2(p), just as before: H(x)=p*log_2(p) P.S: You can type equations in this forum in Latex syntax if you surround them with two$ in the front and back: $$\frac{1}{x}$$ I'm learning in a subject that is called principle of communication II (Hehehe).The dot tip is a good idea,I didn't understood the H(x),you have to make a sum and the PS too,can you try to explain in another way? Thanks RE: define a formula - Stefan - 03-10-2014 01:38 AM (03-10-2014 01:05 AM)fefer92 Wrote:  I didn't understood the H(x) I just wrote the H(x) to indicate that this is the complete formula for the entropy. There is no need to enter the H(x) into the calc. The P.S: instead of including an image for the equations you can write them right away in the text in LaTeX and make two \$ around the equation. So e.g. writing Code: $$\frac{1}{x}$$ leads to $$\frac{1}{x}$$