How does MATLAB's $\tt upfirdn$ select extra points when downsampling?

1. How do you downsample data in Matlab?
2. How do you decimate a signal in Matlab?
3. What is meant by down sampling?

How do you downsample data in Matlab?

y = downsample( x , n ) decreases the sample rate of x by keeping the first sample and then every n th sample after the first. If x is a matrix, the function treats each column as a separate sequence. y = downsample( x , n , phase ) specifies the number of samples by which to offset the downsampled sequence.

How do you decimate a signal in Matlab?

y = decimate( x , r ) reduces the sample rate of x , the input signal, by a factor of r . The decimated vector, y , is shortened by a factor of r so that length(y) = ceil(length(x)/r) .

What is meant by down sampling?

(1) To make a digital audio signal smaller by lowering its sampling rate or sample size (bits per sample). Downsampling is done to decrease the bit rate when transmitting over a limited bandwidth or to convert to a more limited audio format. Contrast with upsample.