merge char and double in matlab

main.m
        Here is an example:

        ```matlab
        str = 'x = ';
        num = 3.14159;
        result = sprintf('%s%f', str, num);
        disp(result);
        ```

        In this example, we first define a `char` array `str` that contains the string "x = ". We then define a `double` value `num` that contains the value of π. We then use the `sprintf` function to merge the `char` array and the `double` value into a single string. The format string `'%s%f'` tells `sprintf` to insert the `char` array `str` (`%s` format specifier) and the `double` value `num` (`%f` format specifier) into the resulting string. 

        The resulting string is stored in the variable `result`, which we then display using the `disp` function. This will output the following text: 

        ```
        x = 3.141590
        ```
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