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Rounding Elements of a Matrix to 3 decimal places

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John hope 2019-4-15

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评论： Star Strider 2019-4-16

Hi all

I'm pulling my hair out with this simple but frustrating issue.

I have two matrices In and Out:-

I am trying to create a new matrix called T which is the subtraction of In and Out.

However i want matrix T to be rounded to 3 dp.

This is what i currently get when i use the round function:-

Can anyone help?

Thank you.

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per isakson 2019-4-15

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See format Set Command Window output display format and try

>> format short

John hope 2019-4-15

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Hi Per

thanks for the input, but it still outputs the matrix values to the default of 4 decimal places.

There must be a command that rounds to 3 decimal places???

Thanks

Star Strider 2019-4-15

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You can try this:

x = rand(5, 1);
format long g
y = round(x, 3)

however it doesn’t truly round to 3 decimal places (you can see that easily enough by using format long rather than format long g), although it looks like it does.

Consider using sprintf if this is important.

Rik 2019-4-15

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It looks like 3 decimal places to me.

I admit I mostly use something like this when I need to round to a number of digits:

k=3;
v=1.8247;
v2=10^k*round(v/10^k);

per isakson 2019-4-15

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>> format short g
>> round( y, 3 )
ans =
        0.815        0.632        0.958
        0.906        0.098        0.965
        0.127        0.278        0.158
        0.913        0.547        0.971

Star Strider 2019-4-15

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It is, although only if you let the format function truncate it and ‘round’ it according to the format function’s internal workings.

An emulation of the most recent implementation of round that I came up with a while ago is:

roundn = @(x,n) round(x .* 10.^n)./10.^n;   % Round ‘x’ To ‘n’ Digits, Emulates Latest ‘round’ Function

It produces results identical to the more recent verisons of round that allow rounding to a specific number of decimal places. If you use format long to view the result, it is not actually rounded, only approximated. The format function then truncates it, depending on the desired result.

John hope 2019-4-16