regressxy: spatial correlation

The spatial correlation of two varaibles can be found with the following ferret script.

This is simply the regresst script re-written to consider space rather than time.

To use this, copy the regressxy script below to a .jnl file and then type

yes? go regressxy
yes? let P = myvar1
yes? let Q = myvar2

in ferret. The variable “corr” is then the spatial correlation between myvar1 and myvar2.

yes? list corr


regressxy.jnl script:

! Description: define FERRET variables for regression along the X and Y axis

say … Linear Regression In the XY Plane
say … Instructions:
say Use the LET command to define new variables
say Define the variable P as your independent (X) variable
say Define the variable Q as your dependent (Y) variable
say Results will be variables “SLOPE”, “INTERCEP” and “RSQUARE”
say QHAT will be the regression estimate
say Note: If “Y” is your independent variable then
say … “SET GRID Q” after defining Q.
say …

let pq = p*q
let pqmask = pq-pq ! 0 or “missing” so all variables share the same missing
let pmasked = p + pqmask
let qmasked = q + pqmask
let pp = pmasked*pmasked
let qq = qmasked*qmasked

let pxave = pmasked[x=@ave]
let qxave = qmasked[x=@ave]
let pave = pxave[y=@ave]
let qave = qxave[y=@ave]
let pqxave = pq[x=@ave]
let ppxave = pp[x=@ave]
let qqxave = qq[x=@ave]
let pqave = pqxave[y=@ave]
let ppave = ppxave[y=@ave]
let qqave = qqxave[y=@ave]
let pvar = ppave – pave*pave
let qvar = qqave – qave*qave
let pqvar = pqave – pave*qave

let slope = pqvar / pvar
let intercep = qave – slope*pave
let qhat = slope*p + intercep
let rsquare = (pqvar*pqvar) / (pvar*qvar)
let corr = pqvar/(pvar*qvar)^0.5


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