How to multiply symbolic with numeric?
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Hi all'
assume that
w=randn(2,2)
a=sym('a',[2 2])
I need to get the answer of multiblication of (a .* w) with smae size [ 2 2] since, I multiplied them like (a .* w) i got this answer
ans =
[ -(4545034027795199*a1_1)/18014398509481984, -(8311781718565711*a1_2)/18014398509481984]
[ -(1390961227654289*a2_1)/1125899906842624, (5388115603050723*a2_2)/18014398509481984]
However, the random values of w is
w =
-0.2523 -0.4614
-1.2354 0.2991
a =
[ a1_1, a1_2]
[ a2_1, a2_2]
I don't belive this correct results however, I need the results like this [ -0.2523 * a1_1, -0.4614* a1_2
-1.2354 * a2_1, 0.2991 * a2_2]
thanks indeed
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Walter Roberson
2020-12-21
w = round(sym(randn(2,2),'d'),4)
You are, by the way, not correct about what the value of w is. The actual values for w extend to about 15 significant decimal places, and you are getting confused because you have the default format in effect. I recommend that you use
format long g
and change your preferences to use that.
However, you defined your required output in terms of four decimal places, so I included a call to force four decimal places.
Note: symbolic floating point numbers give the strong impression that they are base 10 internally, but closer to the truth is that they use a base 2^30 representation, which is close enough to base 10^10 representation that it takes real effort to prove the difference.
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Walter Roberson
2020-12-23
Taking one derivative of one entry of dL4 took my system about 18 minutes. You have over 65000 derivatives to take at the bottom of your code, each on a value that is more complicated than dL4 is. You would expect a minimum of 20 minutes per derivative, times 65000 derivivates, gives about 130000 minutes -> over 900 days.
Each derivative looks like it is going to be over 2 gigabytes to write out -> 130 petabytes .
Suppose that I whipped up something to run on distributed AWS and (somehow!!) managed to create that 130+ petabyte file tomorrow: what would you do with it?
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