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1 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim

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2 1.FUNCTION SUMMARY polyfun Polynomial functions are located in the MATLAB polyfun directory. For a complete list, brief descriptions, and links to reference pages, type: >> help polyfun The following table lists the MATLAB polynomial functions. FunctionDescription conv Multiply polynomials deconv Divide polynomials poly Polynomial with specified roots polyder Polynomial derivative polyfit Polynomial curve fitting polyval Polynomial evaluation polyvalm Matrix polynomial evaluation residue Partial-fraction expansion (residues) roots Find polynomial roots Eng. Mohamed El-Taher Eng. Ahmed Ibrahim

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3 2.REPRESENTING POLYNOMIALS MATLAB software represents polynomials as row vectors containing coefficients ordered by descending powers. For example, consider the equation This is the celebrated example Wallis used when he first represented Newton's method to the French Academy. To enter this polynomial into MATLAB, use p = [1 0 -2 -5];

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4 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim 3.EVALUATING POLYNOMIALS The polyval function evaluates a polynomial at a specified value. To evaluate p at s = 5, use >>polyval(p,5) ans = 110 It is also possible to evaluate a polynomial in a matrix sense. In this case becomes, where X is a square matrix and I is the identity matrix. For example, create a square matrix X and evaluate the polynomial p at X: >> X = [2 4 5; -1 0 3; 7 1 5]; >> Y = polyvalm(p,X) Y= 377 179 439 111 81 136 490 253 639

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5 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim 4.ROOTS roots The roots function calculates the roots of a polynomial: >>r = roots(p) r = 2.0946 -1.0473 + 1.1359i -1.0473 - 1.1359i poly By convention, the MATLAB software stores roots in column vectors. The function poly returns to the polynomial coefficients:: >> p2 = poly(r) >> p2 = 1 8.8818e-16 -2 -5 poly and roots are inverse functions.

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6 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim 5.DERIVATIVES polyder The polyder function computes the derivative of any polynomial. To obtain the derivative of the polynomial p = [1 0 -2 -5], >> q = polyder(p) q = 3 0 -2 polyder also computes the derivative of the product or quotient of two polynomials. For example, create two polynomials a and b: >> a = [1 3 5]; >> b = [2 4 6]; Calculate the derivative of the product a*b by calling polyder with a single output argument: >> c = polyder(a,b) >> c = 8 30 56 38

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7 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim polyder Calculate the derivative of the quotient a/b by calling polyder with two output arguments: >> [q,d] = polyder(a,b) q = -2 -8 -2 d = 4 16 40 48 36 Where q/d is the result of the operation.

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8 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim 6.CONVOLUTION conv deconv Polynomial multiplication and division correspond to the operations convolution and deconvolution. The functions conv and deconv implement these operations. Consider the polynomials and To compute their product, >> a = [1 2 3]; b = [4 5 6]; >> c = conv(a,b) c = 4 13 28 27 18

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9 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim Use deconvolution to divide back out of the product: >> [q,r] = deconv(c,a) q = 4 5 6 r = 0 0 0 0 0

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10 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim 7.LAPLACE TRANSFORM Consider the transfer function The numerator vector : Num=[b0b1..bn] The denominator vector: dem=[1a1..an] The command : [r,p,k]=residue (num,den) The partial fraction expansion is given by Where r : residue, p : poles of the system and k :direct terms of partial fraction 7.1 Partial fraction expansions

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11 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim Consider the transfer function >> b = [-4 8]; a = [1 6 8]; [r,p,k] = residue(b,a) r = -12 8 p = -4 -2 k = []

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12 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim Given three input arguments (r, p, and k), residue converts back to polynomial form: >> [num,den] = residue(r,p,k) b2 = -4 8 a2 = 1 6 8 The command printsys (num,den,‘s’) prints the num/den in terms of the ratio of polynomials in s. num/den = -4 s + 8 ----------------------- s^2 + 6 s + 8

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13 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim The command ilaplace will find the inverse Laplace transform of a Laplace function. -4 s + 8 F(s) = ----------------------- s^2 + 6 s + 8 >> syms s >> f=(-4*s+8)/(s^2+6*s+8) f = -(4*s - 8)/(s^2 + 6*s + 8) >> ilaplace(f) ans = 8/exp(2*t) - 12/exp(4*t) >> pretty (ans) 8 12 -------- - -------- exp(2 t) exp(4 t)

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14 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim Consider the transfer function The MATLAB command [z,p,k] = tf2zp(num,dem) is used to find the zeros, poles, and gain K of B(s)/A(s). If the zeros, poles, and gain K are given, the following MATLAB command can be used to find the original num/den: [num,den] = zp2tf (z,p,k) 7.2 Finding zeros and poles of B(s)/A(s)

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15 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim Given three input arguments (r, p, and k), residue converts back to polynomial form: >> [num,den] = residue(r,p,k) b2 = -4 8 a2 = 1 6 8 The command printsys (num,den,‘s’) prints the num/den in terms of the ratio of polynomials in s. num/den = -4 s + 8 ----------------------- s^2 + 6 s + 8

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16 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim 8.Polynomial Curve Fitting polyfit finds the coefficients of a polynomial that fits a set of data in a least-squares sense: p = polyfit(x,y,n) p = polyfit(x,y,n) x and y are vectors containing the x and y data to be fitted, and n is the degree of the polynomial to return. For example, consider the x-y test data >> x = [1 2 3 4 5]; >> y = [5.5 43.1 128 290.7 498.4]; A third degree polynomial that approximately fits the data is >> p = polyfit(x,y,3) p = -0.1917 31.5821 -60.3262 35.3400

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17 Eng. Mohamed El-Taher Eng. Ahmed Ibrahim Compute the values of the polyfit estimate over a finer range, and plot the estimate over the real data values for comparison: >> x2 = 1:.1:5; >> y2 = polyval(p,x2); >> plot(x,y,'o',x2,y2) >> grid on

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Copyright © 2005. The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Introduction to MATLAB 7 for Engineers William J. Palm.

Copyright © 2005. The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Introduction to MATLAB 7 for Engineers William J. Palm.

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