The algorithm produces an unbiased permutation: every permutation is equally likely. The algorithm effectively puts all the elements into a hat it continually determines the next element by randomly drawing an element from the hat until no elements remain. ![]() The Fisher–Yates shuffle is an algorithm for generating a random permutation of a finite sequence-in plain terms, the algorithm shuffles the sequence. If you have an old version, the code will have a “throw-away” variable (a variable that is not used).Example of shuffling five letters using Durstenfeld's in-place version of the Fisher–Yates shuffle This is a new expansion of the MATLAB language. Notice the use of the tilde character to signify that the first return value isn’t needed. > A(C) % Notice how we use the permutation C to PERMUTE the elements of AĪs this code uses the random number generator ‘rand’, the results you get may be different from these.Īs the original list of numbers is random, it implies that the permutation needed to sort it is a random, uniformly distributed permutation, and this is what MATLAB returns as the output of the function randperm. The function sort normally returns the inputs vector sorted: > sort(rand(1,4))īut if you ask for two output variables, sort will also tell you the permutation needed to get from the input to the output: In this case it is one line of code, but it is slightly strange it turns out that you can return more than one value from a function. Next there’s a long comment block which becomes the help file text (type help randsort and see) and finally the actual body of the function. So whatever the input is when the function is called, internally it will be placed in a variable called n. Now the list of input variables, only one in this case: n. This means that the value of the variable, p when this function terminates, will be returned as the output of the function. Next comes the declaration of the return value p. Notice that the first line starts with the keyword function, which states that this file contains a function rather than a script. % Copyright 1984-2010 The MathWorks, Inc. % random number generator that underlies RAND, RANDI, and RANDN. % Note that RANDPERM calls RAND and therefore changes the state of the % RANDPERM(n) is a random permutation of the integers from 1 to n. It is implemented in MATLAB and can be viewed by writting open randperm (your copy of MATLAB might have a different implementation, but here’s mine): function p = randperm(n) For example the function randperm(n) returns a random ordering of the numbers 1:n. The function sin is not written in MATLAB code, so we cannot see how it is implemented, though on occasion it can be useful to see how some MATLAB functions are implemented. We gave the input pi/2 to the function sin and assigned the output to the variable a. When we “call” a function we usually give it input and expect output. Has very restricted interaction with the caller So what’s a function and how is it different from a script?Ī function is also a file with lines of code, but there are several distinctions between a function and a script: We have also seen scripts files, in which we can put many lines of code and then “call” the script to have MATLAB® execute the lines in that script. This notation can only have one line of code, and oftentimes that can be insufficient for the task at hand. We have just seen-above, using the notation-an example of how to create simple user-defined functions. ![]() Vectorization and User-Defined Functions User-Defined Functions
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