You could use for loops to start at the peak and then start traveling the signal to the right and left until the peak starts to turn around (get smaller). For example, for peak (valley) 2:
% If the peak is at index 150
% Scan to the right.
for k = 151:length(signal)
if signal(k) < signal(k-1)
% Signal is starting to fall.
rightIndex = k-1;
break;
end
end
% Scan to the left.
for k = 149: -1 : 1
if signal(k) < signal(k+1)
% Signal is starting to fall.
leftIndex = k+1;
break;
end
end
peakWidth = rightIndex - leftIndex;
