multiplication

I would like to multiply multiple matrices of a list. I know that this works with a single matrix: x1 <- c(2,2,2,3,1,2,4,6,1,2,4) y1 <- c(5,4,3,3,4,2,1,6,4,2,3) x2 <- c(8,2,7,3,1,2,2,2,1,2,6) y2 <- c(1,3,3,3,1,2,4,3,1,2,8) x3 <- c(1,0,1,0,0,0,1,1,1,1,1) y3 <- c(1,0,0,0,0,0,1,1,0,1,0) x4 <- c(1,0,1,0,0,0,0,1,0,1,0) y4 <- c(1,0,1,0,0,0,1,1,1,1,1) mat1 <- cbind(x1,y1,x2,y2); mat1 mat2 <- cbind(x3,y3,x4,y4); mat2 mat3 <- mat1*mat2; mat3 The result is as I wished, when the second matrix had a zero, then the value was set to zero in the result, otherwise the result was kept the same: x1 y1 x2 y2 [1,

We are doing some 32bit * 32bit multiplication using the following algorithm Let us we want to multiply a (32 bit) with b (32 bit), both signed, a = ah * 2^16 + al [ah - Higher 16 bits, al - Lower 16 bits] b = bh * 2^16 + bl [bh - Higher 16 bits, bl - Lower 16 bits] We are effectively doing Result = (al * bl) + (((ah * bl) + (al * bh)) * 2^16) + ((ah * bh) * 2 ^ 32) ~~~ My question, Is their any better way to do this? In any mainstream compiler, the emulation of 64-bit ints on a 32-bit platform will be about as efficient as doing the mutli-step math yourself. But it will be much more reliably

Is there any way to get the high half of the multiplication of two long s in Java? I.e. the part that vanishes due to overflow. (So the upper 64 bits of the 128-bit result) I'm used to writing OpenCL code where the command mul_hi does exactly this: http://www.khronos.org/registry/cl/sdk/1.0/docs/man/xhtml/mul_hi.html Since OpenCL can do it efficiently on my CPU, Java should be able to do so as well, but I can't find how I should do this (or even mimic its behaviour efficiently) in Java. Is this possible in Java, and if so, how? The accepted solution is wrong most of the time (66%), though the

hi, i'm trying to play a little bit with Mat class. I want to do a product element wise between two images, the c++/opencv port of MATLAB immultiply . This is my code: #include <opencv2/core/core.hpp> #include <opencv2/highgui/highgui.hpp> #include "opencv2/imgproc/imgproc.hpp" #include <iostream> using namespace cv; using namespace std; Mat imgA, imgB; Mat imgAB; Mat product; void printMinMax(Mat m, string s) { double minVal; double maxVal; Point minLoc; Point maxLoc; minMaxLoc( m, &minVal, &maxVal, &minLoc, &maxLoc ); cout << "min val in " << s << ": " << minVal << endl; cout << "max val in

Due to the nature of floating-point math , .4 * .4 = 0.16000000000000003 in Julia. I want to get the mathematically correct answer of 0.16 , in a CPU-efficient way. I know round() works, but that requires prior knowledge of the number of decimal places the answer occupies, so it isn't a general solution. Simon Byrne Some options: Use the inbuilt Rational type. The most accurate and fastest way would be 16//100 * 16//100 If you're using very big numbers these might overflow, in which case you can use BigInt s instead, big(16)//big(100) * big(16)//big(100) (you don't actually need to wrap them

I compiled and ran the source code below successfully by omitting the totalFee field. How do I write totalFee into this program so that it will accurately calculate the total fee for each job (rate * time)? Below, you'll see I tried using a method; which generated the error CS0051 (Inconsistent accessibility: parameter type 'Job' is less accessible than method 'AddJobs.TotalPay(Job)'). This source code is in response to the following assignment: "Design a Job class for Harold’s Home Services. The class contains four data fields—Job description (for example, “wash windows”), time in hours to