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单词 simultaneous equations
释义
simultaneous equations

Computer
  • A set of equations that together define an unknown set of values or functions. The term is normally applied to linear algebraic equations.


Electronics and Electrical Engineering
  • A set of equations used in the solution of n linear algebraic equations in n unknowns, having the general form:

    a11x1+a12x2+a13x3++a1nxn=b1a21x1+a22x2+a23x3++a2nxn=b2a31x1+a32x2+a33x3++a3nxn=b3an1x1+an2x2+an3x3++annxn=b

    Cramer’s rule states that the jth unknown is given directly by

    xj=ΔjΔ

    where Δ is the determinant of the matrix of the coefficients aij (i,j = 1, 2, 3,…,n) and Δj is the determinant of the matrix obtained from the matrix of the coefficients aij by replacing the coefficients of the jth column with the coefficients bj (j = 1, 2, 3,…,n). This assumes that the equations are linearly independent, i.e. that Δ ≠ 0.

    The Gaussian elimination technique repeatedly combines different rows such that the original system of equations is transformed into a system of the type shown below. This is achieved by taking the first equation of the original system and multiplying it by a factor such that when added to the second equation the coefficient of x1 is zero. This is repeated but with the third equation and so on until all the coefficients of x1 become zero. With this new set of equations the technique is repeated so that the coefficients of x2 become zero. This is repeated until xn can be solved directly, i.e. αnnxn = βn. Then by a process of back-substitution all the other unknowns can be determined.

    α11x1+α12x2+α13x3++α1nxn=β1α22x2+α23x3++α2nxn=β2α33x3++α3nxn=β3αnnxn=βn

    Gaussian elimination and Cramer’s rule are used extensively in circuit analysis, where the simultaneous equations are formulated using either node or loop analysis: x1 through xn are the unknown node voltages (or mesh currents), aij (i,j = 1, 2, 3…,n) are known admittances (or resistances), and b1 through bn are known source voltages (or currents).


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