@@ -36,6 +36,7 @@ $A=Matrix([
3636[ 0, 1, 0, 0, 0, 0],
3737[ 0, 0, 0, 0, 0, 1]
3838]);
39+ $B=$A->transpose;
3940
4041$null1 = Matrix([[0],[0],[0],[1],[0],[0]]);
4142$null2 = Matrix([[1],[0],[1],[0],[1],[0]]);
@@ -70,13 +71,13 @@ $V4N = PopUp(["?","Yes","No"], "Yes");
7071$multians = MultiAnswer($null1,$null2)->with( singleResult => 1, separator => ', ', tex_separator => ', ', allowBlankAnswers=>0, checker => ~~&basis_checker_columns, );
7172
7273$image1=image("truss-3node-4bar-motion1.png",
73- width=>140,height=>90,tex_size=>900 );
74+ width=>140,height=>90,tex_size=>140 );
7475$image2=image("truss-3node-4bar-motion2.png",
75- width=>140,height=>90,tex_size=>900 );
76+ width=>140,height=>90,tex_size=>140 );
7677$image3=image("truss-3node-4bar-motion3.png",
77- width=>140,height=>90,tex_size=>900 );
78+ width=>140,height=>90,tex_size=>140 );
7879$image4=image("truss-3node-4bar-motion4.png",
79- width=>140,height=>90,tex_size=>900 );
80+ width=>140,height=>90,tex_size=>140 );
8081
8182
8283#######################################
@@ -89,25 +90,25 @@ Consider the following truss system.
8990$BR
9091
9192\{ image( "truss-3node-4bar.png", width=>180, height=>145,
92- tex_size=>900 , extra_html_tags=>'alt="Truss System"' ) \}
93+ tex_size=>180 , extra_html_tags=>'alt="Truss System"' ) \}
9394All bars are vertical or horizontal.
9495
9596$BR
9697$HR
9798$BR
9899
99- Enter the elongation matrix: $BR
100- (in the form "node 1: horiz", "node 1: vert", "node 2: horiz" etc.)$BR
100+ Enter the force-balance matrix (\(B=A^\mathrm{T}\)) : $BR
101+ (in the form "joint 1: horiz", "joint 1: vert", "joint 2: horiz" etc.)$BR
101102
102103$BCENTER
103- \(A = \) \{ $A ->ans_array() \}
104+ \(B = \) \{ $B ->ans_array() \}
104105$ECENTER
105106
106107$BR
107108$HR
108109$BR
109110
110- Compute a basis for the nullspace of \(A \).
111+ Compute a basis for the nullspace of \(B^\mathrm{T} \).
111112$BR
112113$BCENTER
113114Basis = \(\displaystyle \Bigg\lbrace\)
@@ -120,22 +121,22 @@ $BR
120121$HR
121122$BR
122123
123- Match the following vectors with the movements they would represent and
124- state whether they are in the nullspace of \(A\)
124+ Match the following force vectors \(f_m\) with the motions they would induce
125+ and state whether they are in the nullspace of \(A\)
125126$BR
126127
127128\{
128129BeginTable().
129- AlignedRow(["\($V1 \)", "Movement :$BR $SPACE ". $V1M->menu() .
130+ AlignedRow(["\($V1 \)", "Motion :$BR $SPACE ". $V1M->menu() .
130131 "${BR}In nullspace? $BR $SPACE ". $V1N->menu(),
131132 , "\(\qquad\)" ,
132- "\($V2 \)", "Movement :$BR $SPACE ". $V2M->menu() .
133+ "\($V2 \)", "Motion :$BR $SPACE ". $V2M->menu() .
133134 "${BR}In nullspace? $BR $SPACE ". $V2N->menu(),
134135 , "\(\qquad\)" ,
135- "\($V3 \)", "Movement :$BR $SPACE ". $V3M->menu() .
136+ "\($V3 \)", "Motion :$BR $SPACE ". $V3M->menu() .
136137 "${BR}In nullspace? $BR $SPACE ". $V3N->menu(),
137138 , "\(\qquad\)" ,
138- "\($V4 \)", "Movement :$BR $SPACE ". $V4M->menu() .
139+ "\($V4 \)", "Motion :$BR $SPACE ". $V4M->menu() .
139140 "${BR}In nullspace? $BR $SPACE ". $V4N->menu()],
140141 align=>LEFT, separation=>1).
141142 EndTable() \}
@@ -162,7 +163,7 @@ Context()->normalStrings;
162163
163164$showPartialCorrectAnswers = 1 ;
164165
165- ANS( $A ->cmp );
166+ ANS( $B ->cmp );
166167ANS( $multians->cmp );
167168
168169install_problem_grader(~~&std_problem_grader);
@@ -174,6 +175,6 @@ ANS( $V3M->cmp ); ANS( $V3N->cmp );
174175ANS( $V4M->cmp ); ANS( $V4N->cmp );
175176
176177
177- COMMENT('Elongation matrix');
178+ COMMENT('Force-balance matrix: rows are joints, columns are bars ');
178179
179180ENDDOCUMENT();
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