change number of sig figs in a list of numbers

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Michael
Michael 2011-5-24
basically i have a list of numbers, all with the same number of significant figures. an example of a number is :
734504.0749692708
I want to make this number the following: 734504.07
But the important thing is that I do not want to round. Also, I want to actually change the value, not simply how it is displayed. Matlab knows the exact value, and only displays 5 sig figs from the total of 16. I want to completely drop the last 8 figures in order to give me the above number. any way to do this?

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采纳的回答

Matt Fig
Matt Fig 2011-5-24
N = 734504.0749692708
Ns = round(N*100)/100
EDIT Addressing Oleg's concern...
The above keeps two significant decimals. If you instead want to just drop them, then use fix instead. Look at the difference:
N = 7.85999999
Ns1 = round(N*100)/100
Ns2 = fix(N*100)/100
N =
7.85999999
Ns1 =
7.86
Ns2 =
7.85
  2 个评论
Oleg Komarov
Oleg Komarov 2011-5-24
You should change it to fix otherways the following number is rounded:
N = 734504.079;
Matt Fig
Matt Fig 2011-5-24
I would think that 734504.08 would be the correct solution in keeping 2 significant decimals?
If it is desired to just drop any digits after the second decimal, then you are correct...

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更多回答（2 个）

Andrei Bobrov
Andrei Bobrov 2011-5-24
more (EDIT)
N = 734504.0749692708
Ns = fix(N*100)/100
more more
"I want to completely drop the last 8 figures in order to give me the above number."(Michael):
pwr = 10^(8-ceil(log10(N)))
Ns = fix(N*pwr)/pwr
Walter Roberson
Walter Roberson 2011-5-24
It is not possible to store exactly 734504.07 in MATLAB double .
The algorithms that Matt and Andrei posted can only produce approximations of the number you want. For example, Andrei's solution produces the value 734504.069999999948777258396148681640625 . This is not a bug in Andrei's solution, but rather a limitation in what can be represented in MATLAB without using the Fixed Point Toolbox or the Symbolic Math Toolbox.

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