按照官方的說法：Cairo is a vector graphics library with cross-device output support.
翻譯過來，就是cairo是一個支持多種輸出的向量圖形庫。
具體解釋一下，也就是說，cairo是種畫圖的工具庫，他可以向多種設(shè)備上畫圖，比如：
cairo可以輸出到png,可以輸出到pdf，可以輸出到ps，可以輸出到xlib，可以輸出到XCB，可以輸出到win32，以后還要輸出到svg
我們可以展望一下，如果cairo能夠統(tǒng)一linux下所有的畫圖接口，那么，所見所得可能就會成為顯示。
function y_cum = cum2x (x,y, maxlag, nsamp, overlap, flag)
％CUM2X Cross-covariance
％ y_cum = cum2x (x,y,maxlag, samp_seg, overlap, flag)
％ x,y - data vectors/matrices with identical dimensions
％ if x,y are matrices, rather than vectors, columns are
％ assumed to correspond to independent realizations,
％ overlap is set to 0, and samp_seg to the row dimension.
％ maxlag - maximum lag to be computed [default = 0]
％ samp_seg - samples per segment [default = data_length]
％ overlap - percentage overlap of segments [default = 0]
％ overlap is clipped to the allowed range of [0,99].
