search for: dyx

Hello R Community, I'm continuing to work through logistic regression (thanks for all the help on score test) and have come up against a new opposition. I'm trying to compute Somers Dyx as some suggest this is the preferred method to Somers Dxy (Demaris, 1992). I have searchered the [R] archieves to no avail for a function or code to compute Dyx (not Dxy). The overview of Hmisc has mention of Dyx for the rcorr.cens function but this appears to be a misprint because the manual st...

A colleague pointed out the following error in D(): f <- expression(exp(-2*x*y)) Dx <- D(f, 'x') Dy <- D(f,'y') Dxy <- D(Dx, 'y') Dyx <- D(Dy, 'x') Then > Dx # this is right -exp(-2 * x * y) * (2 * y) > Dy # this is right exp(-2 * x * y) * (-2 * x) > Dxy # this is wrong in the sign of the second term!!! -exp(-2 * x * y) * (-2 * x) * (2 * y) + exp(-2 * x * y) * 2 > Dyx # this is also wrong i...

Hi, I posted this message earlier in "Rmetrics" and I don't know whether I posted in the wrong place, so I'm posting it again in Rhelp. I have a function in x and y and let's call it f(x,y). I need to get the Hessian matrix. i.e I need (d^2f/dx^2), (d^2f/dxdy), (d^2f/dydx), (d^2f/dy^2).I can get these using the D function. now I need to evaluste the hessian matrix for

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