Help with looping a function

Hello, I'm newbie to Matlab (coding in general) and I am having difficulty with running a loop. I have a function that was previously given to me (below) that was made to take an xy plot (Time and position/velocity/acceleration) and using the plot and a certain threshold y value find an x value (specific timepoint). I am now trying to do something similar, however, this threshold value (level) is actually an array of timepoints that I am fishing for in my position time data. The problem is that when I try and run the function I am met with the error that the arrays have incompatible sizes. It seems that the level can only be a single value everytime it is ran. So I thought that a loop would be helpful as ideally each time it ran the level would be equal to the next value in the FootStart_time array. In the initial loop below this just recreated the problem as the level was equal to the entire array rather than a single element. I also tried numel and the text in green, but I just kept running into the problem of not being able to have i equal a single value in the FootStart_tRF and then have it loop. Any ideas or pointers on what I'm missing would be appreciated.

for i=(FootStart_tRF) %also tried i=1:(FootStart_tRF) but this didn't work either%
    level=i %how to make level correspond to individual values of FootStart_tRF?%
    FootStart_xRF=FindTime(RFXS,Time, level)
end 

Function:

function FootStart_xRF = FindTime(RFXS,Time,level)
    cxi = find(diff(sign(Time-level)));
    for k = 1:numel(cxi)
        idxrng = max(1,cxi(k)-1) : min(numel(RFXS), cxi(k)+1);
        FootStart_xRF(k) = interp1(Time(idxrng), RFXS(idxrng), level);
    end
end

Answer 1

[T-800]

I figured it out and thought I would put my solution here incase anyone else has the same question.

FootStart_tRF
for i=1:numel(FootStart_tRF)
    level=FootStart_tRF(i)
    FootStart_xRF=FindTime(RFXS,Time, level)
end 

Although this overwrites the FootStart_tRF variable with each loop.

Here's a version that puts all the values in one array (Retotal)

FootStart_tRF
for i=1:numel(FootStart_tRF)
    level=FootStart_tRF(i)
    FootStart_xRF=FindTime(RFXS,Time, level)
    Total(i)=FootStart_xRF
    Retotal=Total.'
end 
function FootStart_xRF = FindTime(RFXS,Time,level)
    cxi = find(diff(sign(Time-level)));
    for k = 1:numel(cxi)
        idxrng = max(1,cxi(k)-1) : min(numel(RFXS), cxi(k)+1);
        FootStart_xRF(k) = interp1(Time(idxrng), RFXS(idxrng), level);
    end
end

[Star Strider]

A slightly more efficient version that produces ‘Retotal’ as a column vector —

for i=1:numel(FootStart_tRF)

FootStart_xRF=FindTime(RFXS,Time, FootStart_tRF(i))

Retotal(i,:)=FootStart_xRF

end

To convert ‘FindTime’ to accept a vector as the ‘level’ argument —

RFXS = linspace(0, 20, 500);
Time = sin(2*pi*RFXS*0.25) + RFXS/15;

levelv = [0.5, 1, 1.5];

FootStart_xRF = FindTime(RFXS,Time,levelv)

FootStart_xRF = 3×11

0.3179 1.7494 4.1437 5.9334 7.9796 10.1114 11.8142 14.2996 15.6350 18.5259 19.4152 0.7927 1.2623 4.4941 5.5669 8.2950 9.7734 12.1229 13.9556 15.9593 18.1341 19.7929 8.7395 9.3159 12.4665 13.5952 16.2726 17.7970 0 0 0 0 0

figure
plot(RFXS, Time)
hold on
    for k = 1:size(FootStart_xRF,1)
        plot(FootStart_xRF(k,:), zeros(size(FootStart_xRF))+levelv(k), 's', 'MarkerSize',7.5)
    end
hold off
grid

function FootStart_xRF = FindTime(RFXS,Time,level)
for k1 = 1:numel(level)
    cxi = find(diff(sign(Time-level(k1))));
    for k2 = 1:numel(cxi)
        idxrng = max(1,cxi(k2)-1) : min(numel(RFXS), cxi(k2)+1);
        FootStart_xRF(k1,k2) = interp1(Time(idxrng), RFXS(idxrng), level(k1));
    end
end
end

This requires only one call to the function, however a loop to plot the rows is still necessary.

To get column vectors for the output, reverse the indices of the output matrix in the function:

FootStart_xRF(k2,k1) = interp1(Time(idxrng), RFXS(idxrng), level(k1));

.