Most efficient way to generate an array around a central value

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De Ar
De Ar 2018-7-19
编辑： Jan 2018-7-19
Hi!
I am trying to span a linearly spaced array around a center value without knowing number of points in the array beforehand. I only have the step size and the lower and upper limits that must not be exceeded. For example, if center = -4,3, stepsize = 2, lower = -7, upper = 3, then the resulting array should be array = [-6.3 -4.3 -2.3 -0.3 1.7].
Is there a way to generate such an array as efficiently as possible (e.g. without while-loops)?
Thanks for all the help in advance!

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Jan
Jan 2018-7-19
编辑：Jan 2018-7-19
A bold guess:
center = -4.3
step = 2
low = -7
high = 3
vhigh = center:step:high;
vlow = center - step:-step:low;
result = [vlow(end:-1:1), vhigh]
Or in one step:
L = low + rem(center - low, step);
H = high - rem(high - center, step);
result = L:step:H
I'm not sure if this is more stable considering rounding errors:
result = linspace(L, H, 1 + (H-L) / step)

更多回答（1 个）

Adam
Adam 2018-7-19
编辑：Adam 2018-7-19
[ flip( center:-stepsize:lower ), ( center + stepsize ):stepsize:upper ];
looks like it would work, though I haven't tested all edge cases and there are probably neater ways.
If you prefer you could just do the simpler:
unique( [ flip( center:-stepsize:lower ), center:stepsize:upper ] );
to get rid of the duplicated centre point, though I imagine it is less efficient.

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