How to create a multidimensional array of fixed dimensions?

xmin = 0; xmax = 200; xincr = 1;
ymin = -25; ymax = 25; yincr = 0.5;
zmin = 0; zmax = 180; zincr = 1;
hmin = -10; hmax = 10; hincr = 0.1;
xvec = xmin : xincr : xmax;
yvec = ymin : yincr : ymax;
zvec = zmin : zincr : zmax;
hvec = hmin : hincr : hmax;
x2xidx = @(xval) round((xval - xmin)/xincr) + 1;
y2yidx = @(yval) round((yval - ymin)/yincr) + 1;
z2zidx = @(zval) round((zval - zmin)/zincr) + 1;
h2hidx = @(hval) round((hval - hmin)/hincr) + 1;
nx = length(xvec); 
ny = length(yvec);
nz = length(zvec);
nh = length(hvec);
M = zeros(nx, ny, nz, nh);
%example of use
M(x2xidx(17), y2yidx(-6.5), z2zidx(93), h2hidx(-4) ) = 1;
[XIDX, YIDX, ZIDX, HIDX] = ind2sub(size(M), find(M));
disp([XIDX, YIDX, ZIDX, HIDX])
disp([xvec(XIDX), yvec(YIDX), zvec(ZIDX), hvec(HIDX)])

You can store by index or you can use the helper functions to convert numeric value to index.

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Walter Roberson 2020-5-9

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xmin = 0; xmax = 10; xincr = 1;
ymin = -5; ymax = 5; yincr = 0.5;
zmin = 0; zmax = 30; zincr = 1;
hmin = -10; hmax = 10; hincr = 0.5;
for x = xmin:xincr:xmax
    for y = ymin:yincr:ymax
        for z = zmin:zincr:zmax
            for h = hmin:hincr:hmax
                disp([x y z h])
            end
        end
    end
end

or

xmin = 0; xmax = 10; xincr = 1;
ymin = -5; ymax = 5; yincr = 0.5;
zmin = 0; zmax = 30; zincr = 1;
hmin = -10; hmax = 10; hincr = 0.5;
xvec = xmin : xincr : xmax;
yvec = ymin : yincr : ymax;
zvec = zmin : zincr : zmax;
hvec = hmin : hincr : hmax;
nx = length(xvec);
ny = length(yvec);
nz = length(zvec);
nh = length(hvec);
for xidx = 1 : nx
    x = xvec(xidx);
    for yidx = 1 : ny
        y = yvec(yidx);
        for zidx = 1 : nz
            z = zvec(zidx);
            for hidx = 1 : nh
                h = hvec(hidx);
                disp([x y z h]);
            end
        end
    end
end

If you are going to loop over values instead of doing vectorized calculations, then it is typically much better to loop over the indices, in order to permit you to store at appropriate output locations, such as

output(xidx, yidx, zidx, hidx) = x.^2 - y.^3/3 - (x.*z).^h;

Mariana 2020-5-14

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What if I have a variable step per vector. How will you suggest to find the index?

rmin = 0; rmax = 90; rincr = 0.5;
r2min = 91; r2max = 180; r2incr = 1;
r3min =181.5; r3max = 250 ; r3incr = 1.5;
rvec = rmin : rincr : rmax;
r2vec = r2min : r2incr : r2max;
r3vec = r3min : r3incr : r3max;
relx = single([rvec,r2vec,r3vec]);

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Answer 2

Steven Lord 2020-5-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/524077-how-to-create-a-multidimensional-array-of-fixed-dimensions#answer_431276

在 MATLAB Online 中打开

There's no such thing as the -25th column in an array in MATLAB, nor is there such a thing as the 1.5th column.

You can make an array with separate coordinates that you can use like indices (though as usual, be careful when performing exact equality comparisons with == on floating-point numbers. What I wrote below is safe because all the numbers in x and y can be represented exactly in double precision.)

x = (-5:5).';
y = (-3:0.5:3);
z = x.^2 + y.^3;
z(x == -4, y == 1.5) % (-4)^2+(1.5)^3

If you tell us a little more detail about what you're trying to do with this array we may be able to offer alternate suggestions.

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Mariana 2020-5-9

This is the kind of the idea that I would like to do. Just to save a value at a specific space of this array. The array has 8 dimensions or 8 indices. How would you suggest to build and add values to this storage array?

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