MATLAB: ‘setprecision’, 24

featureMATLABprecisionsystem_dependent

Why are the two results below the same? I would like to simulate single precision with system_dependent('setprecision' , 24).

>> system_dependent('setprecision', 64)

>> 10000*sqrt(exp(pi))-48104

ans =

0.773809653510398

>> system_dependent('setprecision', 24)

>> 10000*sqrt(exp(pi))-48104

ans =

0.773809653510398

Best Answer

system_dependent('setprecision')... I seem to recall that it only ever had effect on windows and only for some of the older releases. You could find more information on Yair's undocumented-matlab site.

Related Solutions

MATLAB: How to get more than 49 digits of pi in a string

You could always download my HPF toolbox from the file exchange. It will provide 500100 digits of pi.

P = hpf('pi',500000);
cp = disp(P);
numel(cp)
ans =
      500001
      
cp(1:1001)
ans =
    '3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954930381964428810975665933446128475648233786783165271201909145648566923460348610454326648213393607260249141273724587006606315588174881520920962829254091715364367892590360011330530548820466521384146951941511609433057270365759591953092186117381932611793105118548074462379962749567351885752724891227938183011949129833673362440656643086021394946395224737190702179860943702770539217176293176752384674818467669405132000568127145263560827785771342757789609173637178721468440901224953430146549585371050792279689258923542019956112129021960864034418159813629774771309960518707211349999998372978049951059731732816096318595024459455346908302642522308253344685035261931188171010003137838752886587533208381420617177669147303598253490428755468731159562863882353787593751957781857780532171226806613001927876611195909216420198'

So 1000 digits of pi, plus a decimal point.

As I recall, I even computed those digits using HPF itself just to test the tool, and verify it was working correctly. I'm not sure which series I used, but there are many good ones out there if you look carefully. You do need to be working with a tool that can handle high precision arithmetic. A double will not suffice.

Be careful with the last digit reported to make sure it was not rounded. For example, if you do this:

vpa(sym('pi'),1000)

the last 10 digits reported are ...9216420199

However, the true digits of pi in that vicinity run as: ...9216420198938095...

So the last digit reported by vpa is actually rounded up to a 9.

MATLAB: How to drop last N round-off error digits

Hi Ilya,

if you are happy with an output, then use fprintf:

a=sqrt(pi);
fprintf('a = %.14g\n', a)
a = 1.7724538509055

Otherwise: use e.g. eps to find the roundoff digit.

a = sqrt(pi);
e = eps(a);
% how many decimal digits it this?
digits = floor(-log10(e));
% cut off the last two
digits = digits - 2;
% round to this digit
aRound = round(a*10^digits) / (10^digits)
aRound =
 1.772453850905500

Titus

Best Answer

Related Solutions

MATLAB: How to get more than 49 digits of pi in a string

MATLAB: How to drop last N round-off error digits

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