How to input from file?

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For small number of small-sized matrices like you list above, you could do the following.

Create a file named mat.sage that contains:

a=matrix([[1,0,0], 
[0,1,0],
[1,1,1]])

b=matrix([[0,1,0],
[1,0,0],
[0,0,1]])

Then, in your Sage worksheet, use the command load('mat.sage') to read the matrices into memory. You can then begin computing with these matrices. For example, your worksheet might include:

load('mat.sage')
a*b

which gives a result of

[0 1 0]
[1 0 0]
[1 1 1]

For a very large number of matrices, there are a number of ways you might approach this.

1) You could treat it like one huge matrix and read just that one matrix in. Then, you could break it out into smaller matrices. I don't know if this will result in a memory issue or not.

2) You could read the data in from a csv file and then convert the appropriate parts to matrices. (This is what I would do.)