How do I assign a symbolic variable only to change the variable to an array?

Question

Eric Cheatwood 2017-10-23

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https://ww2.mathworks.cn/matlabcentral/answers/362858-how-do-i-assign-a-symbolic-variable-only-to-change-the-variable-to-an-array

评论： Walter Roberson 2017-10-24

Hi, I am having a hard time trying to assign a symbolic variable to the input x. I am wanting to use x later in my code in its symbolic form but at exp1 I would like to assign the variable a value of an array. Any help is greatly appreciated.

    % code
%Prompting for Amplitude and Limits of Interest
        prompt = {'Enter the Value, "A",  from the form A*exp(t). Include Negative Sign if Applicable',...
            'Enter the Numerical Lower Limit Over Which to Plot the Function Segment'...
            'Enter the Numerical Upper Limit Over Which to Plot the Function Segment'};
        prompttitle = 'Information Input';
        defaultans = {'1', '0', '4'};
        answer = inputdlg(prompt, prompttitle, 1, defaultans);
        expamp2 = str2double(answer(1,1));
        explow1 = str2double(answer(2,1));
        exphigh1 = str2double(answer(3,1));
        %Defining Lower and Upper Limits Chosen in Each Iteration
        lowerlimit1 = explow1;
        upperlimit1 = exphigh1;
        Syms t 
        %Decay Constant Prompt
        prompt1 = 'Enter the Decay Constant Using the variable "/*t" and Include Positive or Negative Integers : ';
        %Prompt User to input the decay constant. This was left as a
        %command window input so that maximum variations can be inputted.
        x = input(prompt1);
        %Auto-Defining 'To' Based on Limit Selection
        To = abs(exphigh1 - explow1);
        Tolong = To*100;
        %Defining Horizontal Axis
        t = (explow1:.01:exphigh1);
        %Formatting all variable to final exp form.
        exp1=expamp2*exp(x);
        %Generalizing naming convention for subplots
        amplitude1 = exp1;
        t1 = t;        
        clc

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Eric Cheatwood 2017-10-23

In other words, I would like exp1 to perform calculations on the array of numbers t but I would like x to hold onto the symbolic value of t to be put through a Fourier Series later on. Thanks

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Answer 1

Walter Roberson 2017-10-23

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https://ww2.mathworks.cn/matlabcentral/answers/362858-how-do-i-assign-a-symbolic-variable-only-to-change-the-variable-to-an-array#answer_287345

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Something like,

syms x
X = input(prompt1);
exp1 = subs(expamp2 * exp(x), x, X);

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Eric Cheatwood 2017-10-24

I understand what you are saying. I defined t1 as a 'double' array. x equals some symbolic equation such as '-2*t' so the t is replaced with an array t1 using the subs function to make X but the symbolic equation x can still be used later. I suppose I could equally do the job with subs(x,t,t1) Thanks again.