Double precision and quadruple precision in MATLAB

Question

I want to convert data(double precision,15 decimal points) to data of another type(quadruple precision,34 decimal points). So, I used vpa function like this:

data = sin(2*pi*frequency*time);
quad_data = vpa(data,34);

But, the type of the result is sym, not double. And when I checked each cell of the sym type data, 1x1 sym was created in each cell. I tried to use fft function using 'quad_data', but it didn't work. Is there any solution that I can change the decimal point of double type from 15 to 34?

Answer 1

There is a commercial 3^rd-party toolbox for this purpose, called the Multiprecision Computing Toolbox for MATLAB.

This tool implements many of the mathematical operations you would expect from double inputs, and according to benchmarks on the website, it's much faster than vpa.

Disclosure: I am not affiliated with the creators of this tool in any way, however I can say that we had a good experience with this tool for one of our lab's projects.

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The other suggestion I can give is doing the high-precision arithmetic in an another language\environment to which MATLAB provides interfaces (e.g., C, python, java), and which should have the quad data type implemented.

Answer 2

The only numeric floating point types that MATLAB currently supports is double, single, and half. Extended precision types can be achieved via the Symbolix Toolbox (e.g., vpa) or 3rd party code (e.g., John D'Errico's FEX submission High Precision Floating HPF class). But even then, only a subset of floating point functions will typically be supported. If the function you are trying to use doesn't support the variable type, then you would have to supply your own function.

Also, you are not building vpa objects properly in the first place. Typically you would convert the operands to vpa first and then do arithmetic on them. Doing the arithmetic in double precision first as you are doing with data, and then converting to extended precision vpa, just adds garbage to the values. E.g., set the digits first and then use vpa('pi') to get the full extended precision version of pi as a vpa variable.