# Subtraction of two single-precision arrays reuslts in an integer (?) array

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Paul Fini 2018 年 10 月 1 日
コメント済み: Stephen23 2018 年 10 月 2 日
I have two 512x512 single-precision arrays (frame_1 and frame_2). Typing the name of either of these in the console shows the block of expected 5-digit numbers: 2.1799, -1.1602, 2.7134, 0.6899, ...
When I try to take the difference (frame_diff = frame_2 - frame_1), the displayed frame_diff array now shows as all integers, even though Matlab claims it's also a single (as it should be!). I thought it was just a console display issue, but when I try options such as format shortEng, the frame_diff numbers indeed seem to be integers (or at least rounded floats!).
What gives? I found nothing in the Matlab array subtraction documentation that would explain what's happening here. The same thing happens with minus(frame_1, frame_2), by the way.
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Stephen23 2018 年 10 月 2 日
"the displayed frame_diff array now shows as all integers, even though Matlab claims it's also a single "
There is no contradiction here: some display formats do not show trailing zeros, even for floating point numbers. Try it yourself:
>> format short
>> single(pi)
ans =
3.1416
>> single(3)
ans =
3
>> format shorteng
>> single(pi)
ans =
3.1416e+000
>> single(3)
ans =
3.0000e+000

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### 採用された回答

TAB 2018 年 10 月 2 日
Values in your arrays frame_1 & frame_2 are such that, difference is always a whole number (fraction part is 0). So they appear as integer.
For example:
frame_1(1,1) --> -0.8467
frame_2(1,1) --> 3.1533
frame_1(1,1) - frame_2(1,1) --> -4
frame_1(1,2) --> -5.9399
frame_2(1,2) --> -0.9399
frame_1(1,2) - frame_2(1,2) --> -5
frame_1(1,3) --> 6.8799
frame_2(1,3) --> -4.1201
frame_1(1,3) - frame_2(1,3) --> 11
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Paul Fini 2018 年 10 月 2 日

Thanks, TAB! This hadn't occurred to me, but it may be due to the nature of these two arrays. This gives me some peace of mind that it's the data itself and not some funky Matlab number typing that I didn't understand (that's happened before!).
I'll do some checking to verify on my end and follow up with any questions if needed.

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