How to determine samplenumber for fixed distance-intervals?

I have a Matrix [1 x 70764] that displays total distance (m) covered up until that point.

I want to determine at which samples intervals of 0.5 m are covered for the whole Matrix.

I want to get an output S which displays the samplenumber at which these 0.5 meter intervals have been covered.

So S(1) = 1 --> total distance is 0 S(2) = ? --> total distance is 0.5 S(3) = ? --> total distance is 1

etc. etc.

Thanks a lot already!

Answer 1

[Jos (10584)]

For examples, I prefer integers, so I upscaled everything by a factor 10.

% your data
M = [0 1 4 6 8 10 12 14 16 17 18 19 22 23] % cumulative distance covered
D = 5 ; % distance

% Note that M is strictly monotonically increasing 
Index = 1:numel(M) ;
P = D:D:M(end) 
S = interp1(M, Index, P)  % S(k) would be where we expected P(k) to appear in M
S = ceil(S)               % After (or at) point S(k) we have covered k*D meters or more

[Ot]

Thanks for your answer!

When I run the statements you suggested, I get an error at:

??? Error using ==> interp1 at 261 The values of X should be distinct.

Error in ==> S = interp1(M, Index, P)

why do I get this error? Maybe becuase between some samples no distance was covered? How to fix this? For the best understanding: This data is from a soccer player during a match, so a large variety in speed is present

Already thanks a lot.

[Jos (10584)]

In that case M is not strictly monotonically increasing, causing problems for INTERP1. However, you can safely remove those values.

M = [0 1 4 6 8 8 8 8 8 8 8 8 10 12 14 16]
D = 5

P = D:D:M(end)
Index = 1:numel(M)
dM = diff(M)
q = [true dM>0] % include first distance always
M(q)      % just to show the used ...
Index(q)  % ... values for interp1
S = ceil(interp1(M(q), Index(q), P))

[Ot]

Thanks!

It works