# Editing Symbolic package

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=== Demos and usage examples === | === Demos and usage examples === | ||

− | * '''I'm trying to substitute a double value into an expression. How can I avoid getting "warning: Using rat() heuristics for double-precision input (is this what you wanted?)" | + | * ''' I'm trying to substitute a double value into an expression. How can I avoid getting "warning: Using rat() heuristics for double-precision input (is this what you wanted?)" |

In general, you should be very careful when converting floating point ("doubles") to symbolic variables, that's why the warning is bothering you. | In general, you should be very careful when converting floating point ("doubles") to symbolic variables, that's why the warning is bothering you. | ||

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% have fun and change it if you want to. | % have fun and change it if you want to. | ||

− | f = @(x) x.^2 + 3*x - 1 + 5*x.*sin(x); | + | f=@(x) x.^2 +3*x-1 + 5*x.*sin(x); |

− | % | + | % the next 2 line take the Anonymous function into a symbolic formula |

− | |||

syms x; | syms x; | ||

− | ff = f(x); | + | |

+ | ff=formula(f(x)); | ||

% now calculate the derivative of the function | % now calculate the derivative of the function | ||

− | ffd = diff(ff | + | ffd=diff(ff); |

% and convert it back to an Anonymous function | % and convert it back to an Anonymous function | ||

− | df = function_handle(ffd) | + | df=function_handle(ffd) |

− | % this uses the interval pkg to find all the roots between -15 an 10 | + | % this uses the interval pkg. to find all the roots between -15 an 10 |

− | |||

fzero (f, infsup (-15, 10), df) | fzero (f, infsup (-15, 10), df) | ||