How to build an NJ tree with an IBS distance matrix computed by PLINK?

Question

[yancheer]

I have got an IBS (identity by state) distance matrix (in .mibs format with its corresponding IDs file) computed by PLINK from genomic SNPs of populations. I read from some articles that NJ trees can be obtained from IBS matrix by MEGA, R, PHYLIP, and the other same softwares. But there were always error warning about my input file format. How can I load my IBS matrix into above softwares, and how to build such an NJ tree?

[Joseph Hughes]

What does the file look like?