This is clearly now nothing to do with the Raspberry PI.
And no-one has actually written that the Performance/Dollar ratio of the Pi is simply too small for supercomputers systems with any power. Fine for teaching about it, not fine for actually using it for any decent workload. Also, no-one has mentioned that actually using the GPU speed is fantastically difficult, bordering on impossible, and the time to develop the software to run the proposed system is multiple 10's of man years.
My suggestion to the OP - you need to read up on massively parallel systems - the computer architecture, the software required. Most supercomputers use Intel (or similar chips) on custom boards that provide very fast interconnects, using boards like the Pi, or even ITX style devices simply don't provide the speed on interconnect required.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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