How to write an empty matrix with 4 number of rows and 3 columns. How to write an epmty row vector.

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saurabh 2016-3-9

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评论： Stephen23 2016-3-9

Suppose I want to write a 3-by-4 empty matrix means I want to write an empty matrix with number of rows 3 and number of columns 4.

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Stephen23 2016-3-9

Lets read the MATLAB documentation. isempty says: "An empty array has at least one dimension of size zero, for example, 0-by-0 or 0-by-5". The page Empty Matrices, Scalars, and Vectors says "A matrix having at least one dimension equal to zero is called an empty matrix"

You want a matrix of size 3-by-4. This is not empty.

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Answer 1

Guillaume 2016-3-9

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The definition of an empty matrix is that one of the dimension has size 0. Therefore, by definition a matrix of size 3x4 is not empty. You can initialise a 3x4 for matrix so that all the elements are 0 (with zeros) or Not-A-Number (with nan) but not empty as a matrix must always contain something if it has a size.

If you really need a container of a given size with empty elements you have to use a cell array.

c = cell(3, 4); %empty cell array of size 3x4

Note that cell arrays are less efficient than matrices and a bit more awkward to use. If all you're going to put in the cell array are scalars you're better off using a matrix.

What problem are you trying to solve with empty matrices?