not able to evaluate the value for an equation using the data from a table, table is three columns data

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kaixi gu 2022-9-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1802585-not-able-to-evaluate-the-value-for-an-equation-using-the-data-from-a-table-table-is-three-columns-d

编辑： Seth Furman 2022-9-13

%creat symbol for axial force, length, thickness, displacemnent and width
syms f l t d w
%define governing equations for parameter
stress = f./(t*w)
strain = d./l
%measurement resolution and uncertainty
%zeroth order uncertainty 
%define symbolic data
T = readtable('Intro_specimen 2.txt');
f = T(:,2);
l = 6.125;
t = 0.057;
d = T(:,1);
w = 0.414;
%substitute value into equation
stress = eval(stress);
strain = eval(strain);

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Walter Roberson 2022-9-10

在 MATLAB Online 中打开

stress = eval(stress);

Never eval() a symbolic object. eval() of a symbolic object is not formally defined, but in practice it is equivalent to eval(char(TheSymbolicObject)) . That is a problem because the character representation of symbolic objects is in a computer language that is not MATLAB and is not the internal MuPAD programming language.

syms x real

y = piecewise(3 < x & x < 5, 2, 4)

y =

char(y)

ans = 'piecewise(x in Dom::Interval(3, 5), 2, symtrue, 4)'

x = pi

x = 3.1416

eval(y)

Error using sym/eval
Invalid expression. Check for missing multiplication operator, missing or unbalanced delimiters, or other syntax error. To construct matrices, use brackets instead of parentheses.

... which is happening because "x in Dom::Interval" is not valid MATLAB syntax.

Pulkit 2022-9-13

Try using 'readmatrix' function instead of 'readtable' as readtable outputs table object which is not supported by element wise operations. If problem still presist please share the exact error message you are getting and also type of data in Intro_specimen 2.txt

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Answer 1

Seth Furman 2022-9-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1802585-not-able-to-evaluate-the-value-for-an-equation-using-the-data-from-a-table-table-is-three-columns-d#answer_1052680

编辑：Seth Furman 2022-9-13

在 MATLAB Online 中打开

You just need to change the parentheses-() to curly braces-{} when pulling data of the table.

See https://in.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html

T = array2table(magic(3))

T = 3×3 table

Var1 Var2 Var3 ____ ____ ____ 8 1 6 3 5 7 4 9 2

%creat symbol for axial force, length, thickness, displacemnent and width

syms f l t d w

%define governing equations for parameter

stress = f./(t*w)

stress =

strain = d./l

strain =

%measurement resolution and uncertainty

%zeroth order uncertainty

%define symbolic data

f = T{:,2}; % <-- curly braces instead of parentheses

l = 6.125;

t = 0.057;

d = T{:,1}; % <-- curly braces instead of parentheses

w = 0.414;

%substitute value into equation

stress = eval(stress)

stress = 3×1

42.3765 211.8824 381.3883

strain = eval(strain)

strain = 3×1

1.3061 0.4898 0.6531

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not able to evaluate the value for an equation using the data from a table, table is three columns data

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