problem with symbolic expression
1 visualización (últimos 30 días)
Mostrar comentarios más antiguos
Michal
el 24 de Mayo de 2017
Comentada: Walter Roberson
el 24 de Mayo de 2017
A have some troubles with conversion of character vector to symbolic expression under R2017a:
% character vector
e = '(-1)*(((2.1967)-(x3))*((x4)+(x2)))'
% symbolic expression
sym(e)
Warning: Support of character vectors that are not valid variable names or define a number will be removed in a future release. To
create symbolic expressions, first create symbolic variables and then use operations on them.
> In sym>convertExpression (line 1586)
In sym>convertChar (line 1491)
In sym>tomupad (line 1243)
In sym (line 199)
ans =
(x3 - 2.1967)*(x2 + x4)
How to solve this problem to be fully compatible with future releases?
0 comentarios
Respuesta aceptada
Walter Roberson
el 24 de Mayo de 2017
You cannot solve it to be fully compatible with future releases. You will need to stop doing that.
Or you could cheat:
e = '(-1)*(((2.1967)-(x3))*((x4)+(x2)))'
vars_char = symvar(e);
vars_sym = sym(vars_char);
vars_cell = num2cell(vars_sym);
fun_str = ['@(', strjoin(vars_char, ','), ') ', e];
fun_handle = str2func(fun_str);
result = fun_handle(vars_cell{:});
However, this will not be exactly the same, in that numeric values will be calculated out, and floating point numbers will typically be converted to rational. For example, 'sin(1) + x' would come out as x + 3789648413623927/4503599627370496
2 comentarios
Walter Roberson
el 24 de Mayo de 2017
I would recommend that you create a support case setting out your reasons why your expressions must be strings, and pushing them for a solution.
Every once in a while, they reverse a decision on removing a feature, if the customers establish that the functionality has no practical work-around.
Más respuestas (0)
Ver también
Productos
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!