Can Someone help me solve what is wrong with this code

Question

Echo Lei 2022-10-4

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1817285-can-someone-help-me-solve-what-is-wrong-with-this-code

评论： VBBV 2022-10-6

在 MATLAB Online 中打开

%Use symbolic processing with the variable x

syms x

syms fp(x)

syms Increasing

syms Decreasing

syms Minimum

syms Maximum

syms Inflection

syms CP

%Enconde the function f(x)

f(x) =(1+x^2)/(1-x^2)

f(x) =

%Set the distance to the left/right of the critical point

h=0.01

h = 0.0100

%Find the first derivative of the function

fp(x) = diff(1+(x^2))/(1-(x^2))

fp(x) =

%Solve for the roots of fp

root1 = solve(fp,x)

root1 =

0

%Consider the first critical point only

c=root1(1)

c =

0

%Determine if the function is "Increasing" or "Decreasing" at the right of the critical point

if (fp(c+h)>0)

IoDR = "Increasing"

elseif (fp(c+h)<0)

IoDR = "Decreasing"

end

IoDR = "Increasing"

%Determine if the function is "Increasing" or "Decreasing" at the right of the critical point

if (fp(c-h)>0)

IoDL = "Decreasing"

elseif (fp(c-h)<0)

IoDL = "Increasing"

end

IoDL = "Increasing"

%Use first derivative Test to Determine if the critical point is a "Maximum" point or "Minimum" point.

if IoDL=="Increasing" & IoDR =="Decreasing"

CP= "Maximum"

elseif IoDL=="Decreasing" & IoDR =="Increasing"

CP= "Minimum"

end

%Find the second derivative of the function

fpp(x)= diff(f,2);

%Find the points of inflection of the function by equating the second derivative of the function to zero.

cc = diff(fp,x)

cc(x) =

%Apply Second Derivative Test to check whether the critical point is a "Maximum" point, a "Minimum" point or "Point of Inflection".

if fpp(c) >0

CP2 = "Maximum"

elseif fpp(c)<0

CP2 = "Minimum"

else

CP2 = "Point of Inflection"

end

CP2 = "Maximum"

%GRAPH THE FUNCTION

clf();

g1= ezplot(f);

hold on

grid on

plot(c,f(c), 'r*')

title("Curve Tracing")

text(c+.5,f(c),["("+string(c)+","+string(f(c))+") "+CP ])

Error using sym>convertChar
Character vectors and strings in the first argument can only specify a variable or number. To evaluate character vectors and strings representing symbolic expressions, use 'str2sym'.

Error in sym>tomupad (line 1624)
S = convertChar(x);

Error in sym (line 397)
S.s = tomupad(x);

Error in sym/privResolveArgs (line 1184)
argout{k} = sym(arg);

Error in sym/privBinaryOp (line 1216)
args = privResolveArgs(A, B);

Error in + (line 7)
X = privBinaryOp(A, B, 'symobj::zipWithImplicitExpansion', '_plus');

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Answer 1

VBBV 2022-10-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1817285-can-someone-help-me-solve-what-is-wrong-with-this-code#answer_1066510

编辑：VBBV 2022-10-4

在 MATLAB Online 中打开

%syms CP

Comment this line and try as CP is symbolic. Then you get know whether it's maximum or minimum

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Girbaud 2022-10-6

"try as CP is symbolic"

how would I input this?

VBBV 2022-10-6

In the given code, the if-else condition for IoDL and IoDR variables are not satisfied since they are both increasing. so, output of CP will be unknown. In order to input CP, c and h needs to computed in such a way that condition is satisfied so that CP can be determined either as minimum or maximum strings.

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