I have a data set which contains cell counts across the 250 brain regions in 12 animals. I want to construct a correlation matrix and a graph theoretical model using the grouped lasso correction. However it says my matrix is not positive definite.
I have tried to use the caret package to select correlations above .xx in order to have a positive definite matrix. However, the highest correlation allowed between variables without throwing the error is .5. This reduces the number of columns from 250 to 8, which I can't use. Can anyone help with suggestions on how to move forward? Could this be do to the fact that I have many more variables than observations?