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Mathews Rus sell W. Howell\nmathews@fullerton.edu howell@westmont.edu\n\nCompl imentary software to accompany the textbook:" }}{PARA 258 "" 0 "" {TEXT 257 82 "COMPLEX ANALYSIS: for Mathematics & Engineering, 4th Ed, 2001, ISBN: 0-7637-1425-9" }{TEXT 297 197 "\nJones and Bartlett Publi shers, Inc., 40 Tall Pine Drive, Sudbury, MA 01776\nTel e. (800) 832-0034; FAX: (508) 443-8000, E-mail: mkt@jbpu b.com, http://www.jbpub.com/" }}}{EXCHG {PARA 0 "" 0 "" {TEXT 293 1 "\n" }{TEXT 256 31 "CHAPTER 5 ELEMENTARY FUNCTIONS" }{TEXT 288 2 "\n\n" }{TEXT 256 55 "Section 5.2 Branches of the Complex Logarithm Function" }{TEXT 289 5 "\n\n " }{TEXT -1 33 "In Section 5.1 we show ed that if " }{XPPEDIT 18 0 "w;" "6#%\"wG" }{TEXT -1 42 " is a nonzero complex number the equation " }{XPPEDIT 18 0 "w = exp(z);" "6#/%\"wG- %$expG6#%\"zG" }{TEXT -1 53 " has infinitely many solutions. Because t he function " }{XPPEDIT 18 0 "`exp(z)`;" "6#%'exp(z)G" }{TEXT -1 85 " \+ is a many-to-one function, its inverse (the logarithm) is necessarily \+ multivalued. " }{TEXT 299 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 " " }}{PARA 0 "" 0 "" {TEXT 300 124 "Load Maple's \"cylinderplot\" and \"conformal mapping\" procedures.\nMake sure this is done only ONCE d uring a Maple session.\n" }}{PARA 0 "> " 0 "" {MPLTEXT 1 0 12 "with(p lots):" }{TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}} {EXCHG {PARA 0 "" 0 "" {TEXT 256 38 "Definition 5.2: Multivalued loga rithm" }{TEXT -1 3 " " }}{PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 5 "For " }{XPPEDIT 18 0 "z <> 0;" "6#0%\"zG\"\"!" } {TEXT -1 39 ", we define the multivalued function " }{XPPEDIT 18 0 " log;" "6#%$logG" }{TEXT -1 55 " as the inverse of the exponential fun ction; that is, " }}{PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 5 " " }{XPPEDIT 18 0 "`log(z) = w`;" "6#%+log(z)~=~wG" } {TEXT -1 22 " if and only if " }{XPPEDIT 18 0 "`z = exp(w)`;" "6 #%+z~=~exp(w)G" }{TEXT -1 3 ". " }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT 256 49 "Definition 5.3: Principal value \+ of the logarithm" }{TEXT -1 4 " " }}{PARA 0 "" 0 "" {TEXT -1 0 "" } }{PARA 0 "" 0 "" {TEXT -1 5 "For " }{XPPEDIT 18 0 "z <> 0;" "6#0%\"zG \"\"!" }{TEXT -1 41 ", we define the single-valued function " } {XPPEDIT 18 0 "Log;" "6#%$LogG" }{TEXT -1 45 ", the principal value o f the logarithm, by " }}{PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 5 " " }{XPPEDIT 18 0 "`Log(z) = ln|z| + i Arg(z)`;" "6 #%:Log(z)~=~ln|grz|gr~+~i~Arg(z)G" }{TEXT -1 3 ". " }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }} {PARA 0 "" 0 "" {TEXT -1 32 " The domain for the function " } {XPPEDIT 18 0 "Log;" "6#%$LogG" }{TEXT -1 51 " is the set of all nonz ero complex numbers in the " }{XPPEDIT 18 0 "z;" "6#%\"zG" }{TEXT -1 47 "-plane, and its range is the horizontal strip " }{XPPEDIT 18 0 "` \{w: `;" "6#%%|frw:~G" }{XPPEDIT 18 0 "-pi;" "6#,$%#piG!\"\"" }{TEXT -1 1 "<" }{XPPEDIT 18 0 "`Im(w)` <= pi;" "6#1%&Im(w)G%#piG" }{XPPEDIT 18 0 "`\}`;" "6#%\"|hrG" }{TEXT -1 2 " " }}{PARA 0 "" 0 "" {TEXT -1 7 "in the " }{XPPEDIT 18 0 "w;" "6#%\"wG" }{TEXT -1 31 "-plane. We st ress again that " }{XPPEDIT 18 0 "Log;" "6#%$LogG" }{TEXT -1 58 " is a single-valued function and corresponds to setting " }{XPPEDIT 18 0 "n = 0;" "6#/%\"nG\"\"!" }{TEXT -1 66 " in the above definition. A s we saw in Chapter 2, the function " }{XPPEDIT 18 0 "Arg;" "6#%$ArgG " }{TEXT -1 52 " is discontinuous at each point along the negative " }{XPPEDIT 18 0 "x;" "6#%\"xG" }{TEXT -1 33 "-axis, hence so is the fun ction " }{XPPEDIT 18 0 "Log" "6#%$LogG" }{TEXT -1 61 ". In fact, bec ause any branch of the multi-valued function " }{XPPEDIT 18 0 "arg;" "6#%$argG" }{TEXT -1 121 " is discontinuous along some ray, a corresp onding branch of the logarithm will have a discontinuity along that sa me ray." }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 0 "" }{TEXT 256 21 "Exam ple for Page 170." }{TEXT 290 2 " " }}{PARA 0 "" 0 "" {TEXT 301 4 " \+ " }}{PARA 0 "> " 0 "" {MPLTEXT 1 0 147 "r:='r': t:='t': u:='u': U:=' U': \nv:='v': V:='V': w:='w': x:='x': y:='y':\nw := log(x + I*y):\n`Lo g(z) ` = w;\nw := evalc(log(x + I*y)):\n`Log(z) ` = w;" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 202 "u := proc(x,y) ln(x^2+y^2)/2 end :\nv := proc(x,y) arctan(y,x) end:\n`Log(z) ` = u(x,y) + I*v(x,y);\n U := proc(r,t) ln(r) end:\nV := proc(r,t) t end:\n`z ` = r*exp(I*t );\n`Log(z) ` = U(r,t) + I*V(r,t);" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT 260 22 "To plot the function \+ " }{XPPEDIT 18 0 "U = log(abs(z))" "6#/%\"UG-%$logG6#-%$absG6#%\"zG" } {TEXT 269 25 " we need to solve \nfor " }{XPPEDIT 18 0 "r" "6#%\"rG " }{TEXT 270 20 " as a function of " }{XPPEDIT 18 0 "u" "6#%\"uG" } {TEXT 271 14 " , that is: " }{XPPEDIT 18 0 "r = exp(u)" "6#/%\"rG-%$ expG6#%\"uG" }{TEXT 272 28 " and use a \"cylinderplot.\"\n" } {MPLTEXT 1 0 0 "" }}{PARA 0 "> " 0 "" {MPLTEXT 1 0 147 "cylinderplot(e xp(u) ,t=0..2*Pi,u=-2..1,\n title=`u(x,y) = ln|z| = ln(r)`,\n style= patchnogrid,\n grid=[50,50],\n lightmodel=light1,\n axes=normal);" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT 256 22 "Example 5.3, Page 170." }{TEXT 291 9 " Find " }{XPPEDIT 18 0 "Log(1 + i)" "6#-%$LogG6#,&\" \"\"F'%\"iGF'" }{TEXT 274 7 " and " }{XPPEDIT 18 0 "log(1 + i)" "6#- %$logG6#,&\"\"\"F'%\"iGF'" }{TEXT 273 3 " .\n" }}{PARA 0 "> " 0 "" {MPLTEXT 1 0 98 "w:='w': z:='z':\nz := 1+I:\n`z ` = z;\nw := log(z):\n `Log(z) ` = w;\nw := evalc(log(z)):\n`Log(z) ` = w;" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT 261 40 "The be st we can do for the multivalued " }{XPPEDIT 18 0 "log(1 + i)" "6#-%$ logG6#,&\"\"\"F'%\"iGF'" }{TEXT 275 13 " is to add " }{XPPEDIT 18 0 "i*2*pi*n" "6#**%\"iG\"\"\"\"\"#F%%#piGF%%\"nGF%" }{TEXT 262 3 " .\n" }{MPLTEXT 1 0 0 "" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 120 "w:='w ': z:='z':\nz := 1+I:\n`z ` = z;\nw := log(z) + I*2*Pi*n:\n`log(z) ` = w;\nw := evalc(log(z)) + I*2*Pi*n:\n`log(z) ` = w;" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT 263 20 "The tr ansformation " }{XPPEDIT 18 0 "w = Log(z)" "6#/%\"wG-%$LogG6#%\"zG" } {TEXT 277 22 " maps the punctured " }{XPPEDIT 18 0 "z" "6#%\"zG" } {TEXT 276 27 "-plane slit along the ray\n" }{XPPEDIT 18 0 "y=0" "6#/% \"yG\"\"!" }{TEXT 278 3 " , " }{XPPEDIT 18 0 "x<=0" "6#1%\"xG\"\"!" } {TEXT 279 46 " , one-to-one and onto the horizontal strip " } {XPPEDIT 18 0 "-pi" "6#,$%#piG!\"\"" }{TEXT 264 3 " < " }{XPPEDIT 18 0 "Im(w)" "6#-%#ImG6#%\"wG" }{TEXT 280 2 "< " }{XPPEDIT 18 0 "pi" "6#% #piG" }{TEXT 265 10 " in the " }{XPPEDIT 18 0 "w" "6#%\"wG" }{TEXT 281 55 "-plane.\n\nThe following graph is the image of the disk " } {XPPEDIT 18 0 "abs(z)<=100" "6#1-%$absG6#%\"zG\"$+\"" }{TEXT 284 22 " \+ slit along the ray " }{XPPEDIT 18 0 "y=0" "6#/%\"yG\"\"!" }{TEXT 283 3 " , " }{XPPEDIT 18 0 "x<=0" "6#1%\"xG\"\"!" }{TEXT 282 3 " .\n" }}{PARA 0 "> " 0 "" {MPLTEXT 1 0 257 "f:='f': z:='z':\nf := z -> log(z ):\n`f(z) ` = f(z);\nconformal(f(Re(z)*exp(I*Im(z))), z=0.01-I*3.14..1 00+I*3.14,\n title=`w = log(z)`,\n grid=[13,13],numxy=[13,13],\n sc aling=constrained,\n labels=[` u`,`v `],\n tickmarks=[5,7],\n view =[-4.7..4.7,-3.2..3.2]);" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}} {EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT 256 22 "E xample 5.4, Page 170." }{TEXT 292 3 " " }{TEXT 256 3 "(a)" }{TEXT 294 8 " Find " }{XPPEDIT 18 0 "Log(-e)" "6#-%$LogG6#,$%\"eG!\"\"" } {TEXT 285 3 " .\n" }}{PARA 0 "> " 0 "" {MPLTEXT 1 0 160 "w:='w': z:='z ':\nz := -exp(1):\n`z ` = z;\nw := log(z):\n`Log(z) ` = w;\nw := evalc (log(z)):\n`Log(z) ` = w;\nw := ln(abs(z)) + I*argument(z):\n`ln|z| + \+ I Arg(z) ` = w;" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT 256 3 "(b)" }{TEXT 295 8 " Find " }{XPPEDIT 18 0 "Log(-1)" "6#-%$LogG6#,$\"\"\"!\"\"" }{TEXT 286 3 " .\n" }}{PARA 0 "> " 0 "" {MPLTEXT 1 0 120 "w:='w': z:='z':\nz := -1:\n`z ` = z;\nw \+ := log(z):\n`Log(z) ` = w;\nw := ln(abs(z)) + I*argument(z):\n`ln|z| + I Arg(z) ` = w;" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT 320 1 "\n" }{TEXT 256 22 "Example 5.5, Page 171. " }{TEXT 321 17 " Verify that " }{XPPEDIT 18 0 "Log(z[1]*z[2]) <> \+ Log(z[1]) + Log(z[2])" "6#0-%$LogG6#*&&%\"zG6#\"\"\"F+&F)6#\"\"#F+,&-F %6#&F)6#F+F+-F%6#&F)6#F.F+" }{TEXT 319 3 " .\n" }}{PARA 0 "> " 0 "" {MPLTEXT 1 0 441 "z:='z':\nz1 := -sqrt(3) + I: z[1] = z1;\nz2 := - 1 \+ + I*sqrt(3): z[2] = z2;\nw1 := log(z1) + log(z2):\nlog(z1) = evalc(lo g(z1));\nlog(z2) = evalc(log(z2));\nLog(z[1]) + Log(z[2]) = w1;\nw1 := evalc(w1):\nLog(z[1]) + Log(z[2]) = w1; ` `;\nz3 := z1*z2:\nw3 := log( z3):\nLog(z[1]*z[2]) = w3;\nz4 := evalc(z3):\nw4 := log(z4):\nLog(z[1] *z[2]) = w4;\nw4 := evalc(w4):\nLog(z[1]*z[2]) = w4; ` `;\n`Does Log( z1) + Log(z2) = Log(z1 z2) ?`;\nw1 = w4;\nevalb(w1 = w4);" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT 256 53 "Theorem 5.2 (A fact concerning princip al logarithm) " }{TEXT -1 5 " " }}{PARA 0 "" 0 "" {TEXT -1 0 "" } }{PARA 0 "" 0 "" {TEXT -1 14 "The identity " }{TEXT 302 4 "Log(" } {XPPEDIT 18 0 "z[1]*z[2];" "6#*&&%\"zG6#\"\"\"F'&F%6#\"\"#F'" }{TEXT 303 8 ") = Log(" }{XPPEDIT 18 0 "z[1];" "6#&%\"zG6#\"\"\"" }{TEXT 304 8 ") + Log(" }{XPPEDIT 18 0 "z[2];" "6#&%\"zG6#\"\"#" }{TEXT 305 1 ") " }{TEXT -1 32 " holds true if and only if " }{XPPEDIT 18 0 "-pi; " "6#,$%#piG!\"\"" }{TEXT -1 3 " < " }{TEXT 306 4 "Arg(" }{XPPEDIT 18 0 "z[1];" "6#&%\"zG6#\"\"\"" }{TEXT 307 8 ") + Arg(" }{XPPEDIT 18 0 "z [2];" "6#&%\"zG6#\"\"#" }{XPPEDIT 18 0 "`)` <= pi;" "6#1%\")G%#piG" } {TEXT -1 1 "." }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT 256 51 "Theorem \+ 5.3 (Facts about the multivalued logarithm)" }{TEXT -1 3 " " }} {PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 4 "Let " } {XPPEDIT 18 0 "z[1]" "6#&%\"zG6#\"\"\"" }{TEXT -1 5 " and " }{XPPEDIT 18 0 "z[2]" "6#&%\"zG6#\"\"#" }{TEXT -1 54 " be nonzero complex number s. The multivalued function " }{XPPEDIT 18 0 "log" "6#%$logG" }{TEXT -1 46 " obeys the familiar properties of logarithms: " }}{PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT 322 2 "i." }{TEXT -1 7 " \+ " }{TEXT 308 4 "log(" }{XPPEDIT 18 0 "z[1]*z[2];" "6#*&&%\"zG6#\"\" \"F'&F%6#\"\"#F'" }{TEXT 309 8 ") = log(" }{XPPEDIT 18 0 "z[1];" "6#&% \"zG6#\"\"\"" }{TEXT 310 8 ") + log(" }{XPPEDIT 18 0 "z[2];" "6#&%\"zG 6#\"\"#" }{TEXT 311 5 ") , " }}{PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT 323 3 "ii." }{TEXT -1 6 " " }{TEXT 312 4 "Log(" } {XPPEDIT 18 0 "z[1]/z[2];" "6#*&&%\"zG6#\"\"\"F'&F%6#\"\"#!\"\"" } {TEXT 313 8 ") = Log(" }{XPPEDIT 18 0 "z[1];" "6#&%\"zG6#\"\"\"" } {TEXT 314 8 ") - Log(" }{XPPEDIT 18 0 "z[2];" "6#&%\"zG6#\"\"#" } {TEXT 315 11 ") , and " }}{PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 " " 0 "" {TEXT 324 5 "iii. " }{TEXT -1 4 " " }{TEXT 316 4 "Log(" } {XPPEDIT 18 0 "1/z;" "6#*&\"\"\"F$%\"zG!\"\"" }{TEXT 317 11 ") = - Lo g(" }{XPPEDIT 18 0 "z;" "6#%\"zG" }{TEXT 318 5 "). " }{TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT 256 26 "Page 172, Properties of " }{XPPEDIT 18 0 "Log(z)" "6#- %$LogG6#%\"zG" }{TEXT 256 2 " ." }{TEXT 296 1 "\n" }}{PARA 0 "> " 0 " " {MPLTEXT 1 0 159 "z1 := x1 + I*y1:\nz2 := x2 + I*y2:\nw1 := log(z1): \nw2 := log(z2):\nv3 := v1 + v2:\n`Log(z1) + Log(z2) ` = w3;\nw3 := ev alc(w1 + w2):\n`Log(z1) + Log(z2) ` = w3; ` `;" }}}{EXCHG {PARA 0 "> \+ " 0 "" {MPLTEXT 1 0 235 "z3 := z1*z2:\nz4 := evalc(z1*z2):\nw4 := log( z3):\n`Log(z1 z2) ` = w4;\nw4 := log(z4):\n`Log(z1 z2) ` = w4;\nw4 := \+ evalc(w4):\n`Log(z1 z2) ` = w4;\nw4 := simplify(w4):\n`Log(z1 z2) ` = \+ w4; ` `;\n`Does Log(z1 z2) = Log(z1) + Log(z1) ?`;\nw4 = w3;" }}} {EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT 266 25 "Therefore we will have " }{XPPEDIT 18 0 "Log(z[1]*z[2]) = Lo g(z[1]) + Log(z[2])" "6#/-%$LogG6#*&&%\"zG6#\"\"\"F+&F)6#\"\"#F+,&-F%6 #&F)6#F+F+-F%6#&F)6#F.F+" }{TEXT 267 16 " provided that " }{XPPEDIT 18 0 "arctan(x[1]*y[2] + y[1]*x[2] , x[1]*x[2] - y[1]*y[2]) = arctan( y[1], x[1]) + arctan(y[2] , x[2])" "6#/-%'arctanG6$,&*&&%\"xG6#\"\"\" F,&%\"yG6#\"\"#F,F,*&&F.6#F,F,&F*6#F0F,F,,&*&&F*6#F,F,&F*6#F0F,F,*&&F. 6#F,F,&F.6#F0F,!\"\",&-F%6$&F.6#F,&F*6#F,F,-F%6$&F.6#F0&F*6#F0F," } {TEXT 287 53 " .\nThose pesky arctan's must be taken seriously ! " }}}{EXCHG {PARA 0 "" 0 "" {TEXT -1 0 "" }}}{EXCHG {PARA 0 "" 0 "" {TEXT 268 19 "End of Section 5.2." }}}}{MARK "0 0 0" 31 }{VIEWOPTS 1 1 0 1 1 1803 1 1 1 1 }{PAGENUMBERS 0 1 2 33 1 1 }