What is wrong with my matlab code?Problem $2\mathrm{.}7$

P $=7\mathrm{.}10^3$; $\%$ Applied load in N

E $=1\mathrm{.}5*10^11$; $\%$ Young's modulus in Pa

A $=10^(-2)$; $\%$ Cross$-$sectional area in m$^2$

L $=3$; $\%$ Length of each square in m

W $=4$; $\%$ Width of the rectangle in m

$\%$ Define node coordinates

nodes $=[00$; L $0$; $2*$L $0$; $3*$L $0$; $4*$L $0$; $0$ L; L L; $2*$L L; $3*$L L; $4*$L L$]$;

$\%$ Define element connectivity

elements $=[12$; $23$; $34$; $45$; $16$; $27$; $38$; $49$; $510$; $67$; $78$; $89$; $910]$;

numNodes $=$ size$($nodes$,1)$;

numElements $=$ size$($elements$,1)$;

K $=$ zeros$(2*$numNodes$)$;

F $=$ zeros$(2*$numNodes$,1)$;

for i $=1$:numElements

node$1=$ elements$($i$,1)$;

node$2=$ elements$($i$,2)$;

x$1=$ nodes$($node$1,1)$;

y$1=$ nodes$($node$1,2)$;

x$2=$ nodes$($node$2,1)$;

y$2=$ nodes$($node$2,2)$;

L $=$ norm$([$x$2-$ x$1,$ y$2-$ y$1])$;

cosTheta $=($x$2-$ x$1)/$ L;

sinTheta $=($y$2-$ y$1)/$ L;

k $=($E A $/$ L$)[$cosTheta$^2$ cosTheta$*$sinTheta; cosTheta$*$sinTheta sinTheta$^2]$;

$\%$ Assemble into global stiffness matrix

index $=[2*$node$1-1,2*$node$1,2*$node$2-1,2*$node$2]$;

K$($index$,$ index$)=$ K$($index$,$ index$)+$ k;

$\%$ Apply nodal loads

F$(2*$node$2-1)=$ F$(2*$node$2-1)+$ P $*$ cosTheta;

F$(2*$node$2)=$ F$(2*$node$2)+$ P $*$ sinTheta;

end

penalty $=1$e$9$; $\%$ Adjust this value as needed

fixedNode $=1$; $\%$ Assuming the first node is fixed

K$($fixedNode$*2-1,$ :) $=0$;

K$($:$,$ fixedNode$*2-1)=0$;

K$($fixedNode$*2-1,$ fixedNode$*2-1)=$ penalty;

K$($fixedNode$*2,$ :) $=0$;

K$($:$,$ fixedNode$*2)=0$;

K$($fixedNode$*2,$ fixedNode$*2)=$ penalty;

F$($fixedNode$*2-1)=0$;

F$($fixedNode$*2)=0$;

U $=$ K $\backslash$ F;

stresses $=$ zeros$($numElements$,1)$;

for i $=1$:numElements

node$1=$ elements$($i$,1)$;

node$2=$ elements$($i$,2)$;

x$1=$ nodes$($node$1,1)$;

y$1=$ nodes$($node$1,2)$;

x$2=$ nodes$($node$2,1)$;

y$2=$ nodes$($node$2,2)$;

L $=$ norm$([$x$2-$ x$1,$ y$2-$ y$1])$;

cosTheta $=($x$2-$ x$1)/$ L;

sinTheta $=($y$2-$ y$1)/$ L;

strain $=([$cosTheta sinTheta$][$U$(2$node$2-1)$; U$(2*$node$2)]-[$cosTheta sinTheta$][$U$(2$node$1-1)$; U$(2*$node$1)])/$ L;

stresses$($i$)=$ E $*$ strain;

end

mag $=1000$; $\%$ Magnification factor for better visualization

defNodes $=$ nodes $+$ mag $*$ reshape$($U$,[],2)$;

figure;

hold on;

for i $=1$:numElements

node$1=$ elements$($i$,1)$;

node$2=$ elements$($i$,2)$;

plot$([$nodes$($node$1,1),$ nodes$($node$2,1)],[$nodes$($node$1,2),$ nodes$($node$2,2)],\text{'}$b$-\text{'},$ 'LineWidth', $1)$;

end

for i $=1$:size$($defNodes$,1)$

plot$($defNodes$($i$,1),$ defNodes$($i$,2),\text{'}$ro$\text{'},$ 'MarkerSize', $5)$;

end

xlabel$(\text{'}$x $($m$)\text{'})$;

ylabel$(\text{'}$y $($m$)\text{'})$;

title$(\text{'}$Deformed Structure'$)$;

axis equal;

grid on;