Manipulate Arrays Size using Colon Operator.

I am having trouble using the colon operator properly. I have two variables which will be plotted using the plot command. However, to plot this graph I need each of the vector arrays to have the same number of elements. Below is how I've used the colon operator.

time = min(timeInterval) : 0.001 : max(timeInterval);
signal = min(origSignal) : (max(origSignal) - min(origSignal))/length(time) : max(OrigSignal);

I keep running into the issue that the vector arrays time and signal are not of the same size. Signal is always 1 element smaller than time regardless of what the increment specified in the time array declaration. Any thoughts on how to manipulate the number of elements? Either add a value to the end of the array or delete a value from the end of the larger array.

Thanks for any assistance!

Answer 1

[Walter Roberson]

Consider:

Let both of them be 1:10, which is length(10). min() is 1, max is 10, 10-1 is 9, so the increment becomes 9 / 10. Then 1 : 9/10 : 10 is

1, 19/10, 28/10, 37/10, 46/10, 55/10, 64/10, 73/10, 82/10, 91/10, 10

and that's 11 elements. What increment should be applied, 1 : x : 10 to get 10 elements? Clearly it should be 1.

Look at it algebraically. If the max is to be the t'th element, then min + increment * (t-1) = max, so increment * (t-1) = max-min so increment = (max-min)/(t-1)... but you are dividing by t instead of by t-1.

You should consider using

signal = linspace( min(origSignal), max(origSignal), length(time));

Answer 2

[Dmytri]

I forgot to mention that I'm trying to make a unit step function. I had thought about using the linspace command but it always creates a linear line in the upward direction. That's why I was trying to use the colon operator to help create this unit step function.

If I don't try to increase the resolution of the plot by increasing the number of points it looks like a heaviside function with the exception of where it switches between the lower and upper number. However, once I add more points in between the upper and lower limits of the time array it becomes less of a heaviside function but rather a positive sloped linear function.

Not sure why this happens...

[Walter Roberson]

? The colon operator is always going to produce a monotonic increasing or decreasing list. You cannot use 0 as the increment. If you need a bunch of values repeated then use repmat().