numeric

问题 What's the most succinct, fastest, most numerically stable, most R-idiomatic way to do left and right matrix division in R? I understand left division inv(A)*B is usually done with solve(a,b) , but how about B*inv(A) ? Is the best way really to compute t(solve(t(A),t(B))) ? 回答1: I don't have a solution better than B %*% solve(A) , but I did want to point out that in general solve(A,B) is faster and more numerically stable than solve(A) %*% B . > A = matrix(rnorm(10000),100,100) > B = matrix

问题 I have to extract a number (a measured time value) from each of several strings. How could I do this elegantly? All numbers are positive and have a maximum of two decimal places. (E.g.: 2.3/ 40.09/ 101.4 - no numbers in E notation). The code I am looking for should do something like the following pseudocode: >>> "It took 2.3 seconds".strip(everything but ".1234567890") 2.3 回答1: Instead of strip, select for the numbers with a regular expression: import re numbers = re.compile('\d+(?:\.\d+)?')

问题 I have vales with very small difference like... 0.000001. I want to visualize them on logarithmic scale. I am wondering how to do it in matplotlib. Thanks a lot 回答1: http://matplotlib.sourceforge.net/api/pyplot_api.html#matplotlib.pyplot.axis Simply add the keyword argument log=True Or, in an example: from matplotlib import pyplot import math pyplot.plot([x for x in range(100)],[math.exp(y) for y in range(100)] ) pyplot.xlabel('arbitrary') pyplot.ylabel('arbitrary') pyplot.title('arbitrary')

问题 Does anyone know of a reliable, accurate library to compute the multivariate normal (MVN) CDF in Java? I'm looking for something like MATLAB's mvncdf function. I need to be able to do it for dimensions of up to 10 or more. Most statistics/math libraries don't have this functionality. Being able to compute the log probability is a plus. From this post, there doesn't seem to be a free implementation mentioned for some other languages. While a straight-java implementation would rock, I would

问题 How can I create a numeric text box in java swing , which has two buttons (up and down) which increments and decrements the value in the text box respectively. Also this text box must be editable with ONLY NUMERIC VALUES . Something like this I tried by placing two buttons near a text box and manually doing the operation on button click. Is there any other method in which I can do this in a better way and achieve a similar result as the first image. Thanks :) 回答1: Use JSpinner How to use

问题 I have two different arrays. One array, a, for a list of people. My other array, b, for a list of their ages. I go to sort b by number and then reverse it so it goes in descending order. I got to this part okay. How do I sort a (a list of people's names) so that the same values are still paired up with the sorted list? Example: a contains Bob, Sue, Phil, and Jenny respectively b contains 15, 12, 13, and 13 respectively. I want my outcome to be: a contains Bob, Jenny, Phil, and Sue

问题 I just read an interesting article about php hanging on certain float numbers, see The Register and Exploring Binary. I never explicitly use floats, I use number_format() to clean my input and display for example prices. Also, as far as I am aware, all input from for example forms are strings until I tell them otherwise so I am supposing that this problem does not affect me. Am I right, or do I need to check for example Wordpress and Squirrelmail installations on my server to see if they cast

问题 I need to write a function that rounds from unsigned long long to float, and the rounding should be toward nearest even. I cannot just do a C++ type-cast, since AFAIK the standard does not specify the rounding. I was thinking of using boost::numeric, but i could not find any useful lead after reading the documentation. Can this be done using that library? Of course, if there is an alternative, i would be glad to use it. Any help would be much appreciated. EDIT: Adding an example to make

问题 I have a convolution integral of the type: To solve this integral numerically, I would like to use numpy.convolve() . Now, as you can see in the online help, the convolution is formally done from -infinity to +infinity meaning that the arrays are moved along each other completely for evaluation - which is not what I need. I obviously need to be sure to pick the correct part of the convolution - can you confirm that this is the right way to do it or alternatively tell me how to do it right and

问题 I am getting the error: Warning: invalid value encountered in log From Python and I believe the error is thrown by numpy (using version 1.5.0). However, since I am calling the "log" function in several places, I'm not sure where the error is coming from. Is there a way to get numpy to print the line number that generated this error? I assume the warning is caused by taking the log of a number that is small enough to be rounded to 0 or smaller (negative). Is that right? What is the usual