How can I make a program which uses all cores and 100% of cpu power?

[Murilo via Digitalmars-d-learn]

I have started working with neural networks and for that I need a 
lot of computing power but the programs I make only use around 
30% of the cpu, or at least that is what Task Manager tells me. 
How can I make it use all 4 cores of my AMD FX-4300 and how can I 
make it use 100% of it?