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Solving 7x7 Matrix Returns Very Long Fractions

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balsip
balsip 2016년 10월 12일
댓글: Steven Lord 2016년 10월 13일
Hello, I'm solving a 7x7 matrix. After inputting the A matrix and B vector and solving, the returned solutions for X are very, very long fractions. How can I specify that I would like these returned in rounded numbers (in scientific notation, for example), not in fractions? Code is below, and thank you.
Cx = 6 + 0.0806;
Cy = 6.8359;
syms w1 w2 w3 w4 w5 w6 w7;
eqn1 = + ((Cx)*w1) - (4*w2) + (1*w3) + (0*w4) + (0*w5) + (0*w6) - (4*w7) == (Cy)*(2*.125);
eqn2 = - (4*w1) + ((Cx)*w2) - (4*w3) + (1*w4) + (0*w5) + (0*w6) + (0*w7) == (Cy)*sin(2*pi*.250);
eqn3 = + (1*w1) - (4*w2) + ((Cx)*w3) - (4*w4) + (1*w5) + (0*w6) + (0*w7) == (Cy)*sin(2*pi*.375);
eqn4 = + (0*w1) + (1*w2) - (4*w3) + ((Cx)*w4) - (4*w5) + (1*w6) + (0*w7) == (Cy)*sin(2*pi*.500);
eqn5 = + (0*w1) + (0*w2) + (1*w3) - (4*w4) + ((Cx)*w5) - (4*w6) + (1*w7) == (Cy)*sin(2*pi*.625);
eqn6 = + (0*w1) + (0*w2) + (0*w3) + (1*w4) - (4*w5) + ((Cx)*w6) - (4*w7) == (Cy)*sin(2*pi*.750);
eqn7 = - (4*w1) + (0*w2) + (0*w3) + (0*w4) + (1*w5) - (4*w6) + ((Cx)*w7) == (Cy)*sin(2*pi*.875);
[A,B] = equationsToMatrix([eqn1, eqn2, eqn3, eqn4, eqn5, eqn6, eqn7], [w1, w2, w3, w4, w5, w6, w7]);
X = linsolve(A,B)
This returns the following (only w1 solution showing due to length):
X = 2182838934989084222859735148265186349320750668882016039009/735711874176482141060943596914818753670316261979795226624

채택된 답변

Walter Roberson
Walter Roberson 2016년 10월 12일
Use vpa() or double() on the answer
  댓글 수: 4
balsip
balsip 2016년 10월 13일
편집: balsip 2016년 10월 13일
That was entirely unintended. It seems like the symbolic variables are the default output of the linsolve() function.
Steven Lord
Steven Lord 2016년 10월 13일
Only when you pass symbolic variables into linsolve.
A = gallery('minij', 7);
b = sum(A, 2);
xd = linsolve(A, b); % double
xs = linsolve(sym(A), b); % sym
whos xd xs

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