How do you vectorize the following code? i = 0 Later on in this course, we will see that MATLAB has inherited these excellent vectorization techniques and syntax for matrix calculations from its high-performance ancestor, Fortran.
#Matlab vectorize code
Now doing the same thing, using array notation would yield, > tic, s = sum(x.^2) tocĪmazing! isn’t it? You get almost 3x speedup in your MATLAB code if you use vectorized computation instead of for-loops. > tic, s = 0 for i=1:n, s = s + x(i)^2 end, toc For example, consider the process of summation of a random vector in MATLAB, > n = 5e7 x = randn(n,1) Furthermore, it expresses algorithms in terms of high-level constructs that are more appropriate for high-performance computing. It can lead to shorter and more readable MATLAB code. Vectorization has important benefits beyond simply increasing speed of execution. One of the most important tips for producing efficient M-files is to avoid for -loops in favor of vectorized constructs, that is, to convert for-loops into equivalent vector or matrix operations. Relatively slowly-depending on what is inside the loop, MATLAB may or may notīe able to optimize the loop. This is true of the arithmetic operators *, +, -, \, / and of relational and logical operators. Since MATLAB is a matrix language, many of the matrix-level operations and functions are carried out internally using compiled C, Fortran, or assembly codes and are therefore executed at near-optimum efficiency. There is of course, a remedy for this inefficiency. There is a reason for this: for-loops and while-loops have significant overhead in interpreted languages such as MATLAB and Python. When nesting a number of while statements, each while statement requires an end keyword.Įxperienced programmers who are concerned with producing compact and fast code try to avoid for loops wherever possible in their MATLAB codes.To skip the rest of the instructions in the loop and begin the next iteration, use a continue statement. To exit the loop, use a break statement as discussed above.To execute statements if any element is true, wrap the expression in the any() function. If the conditional expression evaluates to a matrix, MATLAB evaluates the statements only if all elements in the matrix are true (nonzero).If you inadvertently create an infinite loop (that is, a loop that never ends on its own), stop execution of the loop by pressing Ctrl+C.Write function getFac(n) using while-loop, that calculates the factorial of an input number n. It’s good practice to include some diagnostic output or other indication that an abnormal loop exit has occurred once the code reach the break statement. For example, n = 0 Ī break immediately jumps execution to the first statement after the loop. This can be done in a number of ways, but the most common is to use break.
It’s often a good idea to limit the number of repetitions to avoid infinite loops (as could happen above if x is infinite). The condition is evaluated before the body is executed, so it is possible to get zero iterations. Note that, break and continue can be used in while-loops in the same fashion as they are used in for-loops, described above. Write a function that does so, using for-loop, break, and MATLAB’s intrinsic function isprime().Īnswer: function integer = getPrime(upper) Suppose you want to find the largest prime number that is smaller than a given input value by the user. This is specially useful when you want to ensure if a condition has happened, and if so, then terminate the for-loop.
#Matlab vectorize full
You can also use break inside a for-loop to get out of it, even before the for-loop finishes the full number of iterations. You can also iterate in reverse order, > istart = 10 For example consider a script named forLoop.m, for index = istart:stepSize:iendĭisp( ) The statements are the set of programming tasks that have to be repeated. Usually, expression is a vector of the form istart:stepSize:iend where fix((iend-istart)/stepSize+1) gives the number of iterations requested by the user, assuming iend>istart. The general syntax of for-loop is, for variable = expression The for-loop is among the most useful MATLAB constructs. Similar to other programming languages, MATLAB also has built-in tools for iterative tasks in codes.
Many programming algorithms require iteration, that is, the repetitive execution of a block of program statements.
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