[R] Checking if a matrix exists/is defined

[Steven Yen]

Hello
Can someone help me with the following, specifically in judging 
whether a matrix exists. I have trouble with the first line below. In 
this case, matrix obj$hessian exists and is 74 x 74. I receive the 
error message:

Warning message:
In all(w$hessian) : coercing argument of type 'double' to logical

Thank you all.

---
if (!all(obj$hessian)|OPG){
   vb<-obj$gradientObs; vb<-solve(t(vb)%*%vb)
   vb.method<-"; v(b)=inv(G'G)"
} else {
   vb<- solve(-obj$hessian)
   vb.method<-"; v(b)=inv(-H)"
} 
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