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# Rounding entries of a matrix

Given a matrix with real entries, how can I display that matrix with all entries rounded to a particular number of decimal places? The "round" function doesn't seem to work when you call a matrix instead of a scalar value.

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## 3 Answers

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m=matrix(RR,3,range(9));m

[0.000000000000000  1.00000000000000  2.00000000000000]
[ 3.00000000000000  4.00000000000000  5.00000000000000]
[ 6.00000000000000  7.00000000000000  8.00000000000000]

m.n(digits=4)

[0.0000  1.000  2.000]
[ 3.000  4.000  5.000]
[ 6.000  7.000  8.000]

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Alternative : the apply_map method :

sage: M=matrix([u/13 for u in range(9)], ncols=3) ; M
[   0 1/13 2/13]
[3/13 4/13 5/13]
[6/13 7/13 8/13]
sage: M.apply_map(lambda u:round(u,2))
[ 0.0 0.08 0.15]
[0.23 0.31 0.38]
[0.46 0.54 0.62]


HTH,

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One way is to use less accurate floating point numbers.

This can be done using

• the method change_ring of a matrix
• the function RealField

Define a matrix:

sage: a = matrix(RR, 3, [j * 100./99 for j in (1 .. 9)])
sage: a
[1.01010101010101 2.02020202020202 3.03030303030303]
[4.04040404040404 5.05050505050505 6.06060606060606]
[7.07070707070707 8.08080808080808 9.09090909090909]


Change to 20-bit floating point numbers

sage: b = a.change_ring(RealField(20))
sage: b
[1.0101 2.0202 3.0303]
[4.0404 5.0505 6.0606]
[7.0707 8.0808 9.0909]

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Asked: 2023-01-11 18:54:37 +0100

Seen: 346 times

Last updated: Jan 12 '23