Solve systems of linear equations Ax = B for x

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Johan Johan
Johan Johan el 29 de Ag. de 2019
Editada: Stephen23 el 29 de Ag. de 2019
x = A\B solves the system of linear equations A*x = B. The matrices A and B must have the same number of rows.
But ,what is the operation between the rows?
There is any one can solve this example–manually ?
A =
1 3
4 2
b= [6 ;7];
>> A\b
ans =
0.9000
1.7000
How to find 0.9 and 1.7 exactly?

Respuesta aceptada

Stephen23
Stephen23 el 29 de Ag. de 2019
Editada: Stephen23 el 29 de Ag. de 2019
"But ,what is the operation between the rows?"
Both mldivide and mrdivide can use many different algorithms for solving systems of linear equations, as documented in the mldivide documentation. There is no single "operation" that describes all of those algorithms.
"There is any one can solve this example–manually ?"
This is easy using standard definitions for solving linear equations, e.g. elimination of variables:
System definition:
First solve the first equation for x:
Second, substitute x back into the second equation:
Third, solve that for y:
And finally try them with your example values:
>> A = [1,3;4,2]
A =
1 3
4 2
>> b = [6;7]
b =
6
7
>> A\b
ans =
0.9
1.7
>> y = (A(1,1)*b(2)-A(2,1)*b(1)) ./ (A(1,1)*A(2,2)-A(2,1)*A(1,2))
y =
1.7
>> x = (b(1)-A(1,2)*y) ./ A(1,1)
x =
0.9

Más respuestas (2)

KALYAN ACHARJYA
KALYAN ACHARJYA el 29 de Ag. de 2019
Editada: KALYAN ACHARJYA el 29 de Ag. de 2019
ans =
0.9000
1.7000
How to find 0.9 and 1.7 exactly??
format shortg;
A =[1 3
4 2];
b= [6 ;7];
A\b
Result:
ans =
0.9
1.7

Torsten
Torsten el 29 de Ag. de 2019
https://en.wikipedia.org/wiki/Cramer%27s_rule

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