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Symbolic package: Difference between revisions
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(→Demos and usage examples: rework the evaluate-at-double example) |
(copy edit for demo) |
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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); | ||
% | % these next lines take the Anonymous function into a symbolic formula | ||
pkg load symbolic | |||
syms x; | syms x; | ||
ff = f(x); | |||
ff= | |||
% now calculate the derivative of the function | % now calculate the derivative of the function | ||
ffd=diff(ff); | ffd = diff(ff, x); | ||
% 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 | % this uses the interval pkg to find all the roots between -15 an 10 | ||
pkg load interval | |||
fzero (f, infsup (-15, 10), df) | fzero (f, infsup (-15, 10), df) | ||