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Unformatted text preview: Symbolic Computations CSC 113 Fall 2010 Conventional Computations Matlab was designed to execute serial computations: value = expression; For example, suppose we have D = D e Q / RT If we know the values on the righthand side, we can calculate D : >> D0 = 25; >> Q = 1.6e 19; >> R = 10; >> T = 273; >> D = D0 * exp (Q /( R*T )); What if instead we know everything except T ? On paper, we could proceed as follows: D = D e Q / RT ln ( D ) = ln ( D ) Q RT ln D D = Q RT T = Q R ln ( D / D ) Can we coerce Matlab into solving for one variable in terms of the others? This is the purpose of symbolic computation (requires the symbolic toolbox, which uses Maple). What if instead we know everything except T ? On paper, we could proceed as follows: D = D e Q / RT ln ( D ) = ln ( D ) Q RT ln D D = Q RT T = Q R ln ( D / D ) Can we coerce Matlab into solving for one variable in terms of the others? This is the purpose of symbolic computation (requires the symbolic toolbox, which uses Maple). Symbolic Variables Symbolic variables look like strings, but can be manipulated according to standard rules of algebra. To define a symbolic variable, use either sym('expression') or syms variables . Examples: >> syms x >> y = 2*( x +3)^2/( x ^2+6* x +9) Alternatively, >> y = sym ( '2*( x +3)^2/( x ^2+6* x +9) ') This does not assign values to x or y , but rather assigns their functional dependence . Let’s return to the earlier equation: D = D e Q...
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 Fall '10
 PhillipRegali
 Expression, sym, symbolic variables

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