define 300 function calls x1(t)---x300(t)

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Tony Cheng
Tony Cheng on 24 Aug 2025
Edited: Torsten on 1 Oct 2025 at 18:57
Hi there,
I am using ode15s to resolve a DAE system. Since there are 300 variables x1(t)~x300(t) in my case, so I feel it is a little bit inconvenient to define them by writing
syms x1(t) … x300(t)
one by one. Are there any efficient codes to define them?
Many thanks!

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Accepted Answer

Walter Roberson
Walter Roberson on 24 Aug 2025
Ran in:
syms x(t) [1 300]
whos
Name Size Bytes Class Attributes t 1x1 8 sym x 1x1 8 symfun x1 1x1 8 symfun x10 1x1 8 symfun x100 1x1 8 symfun x101 1x1 8 symfun x102 1x1 8 symfun x103 1x1 8 symfun x104 1x1 8 symfun x105 1x1 8 symfun x106 1x1 8 symfun x107 1x1 8 symfun x108 1x1 8 symfun x109 1x1 8 symfun x11 1x1 8 symfun x110 1x1 8 symfun x111 1x1 8 symfun x112 1x1 8 symfun x113 1x1 8 symfun x114 1x1 8 symfun x115 1x1 8 symfun x116 1x1 8 symfun x117 1x1 8 symfun x118 1x1 8 symfun x119 1x1 8 symfun x12 1x1 8 symfun x120 1x1 8 symfun x121 1x1 8 symfun x122 1x1 8 symfun x123 1x1 8 symfun x124 1x1 8 symfun x125 1x1 8 symfun x126 1x1 8 symfun x127 1x1 8 symfun x128 1x1 8 symfun x129 1x1 8 symfun x13 1x1 8 symfun x130 1x1 8 symfun x131 1x1 8 symfun x132 1x1 8 symfun x133 1x1 8 symfun x134 1x1 8 symfun x135 1x1 8 symfun x136 1x1 8 symfun x137 1x1 8 symfun x138 1x1 8 symfun x139 1x1 8 symfun x14 1x1 8 symfun x140 1x1 8 symfun x141 1x1 8 symfun x142 1x1 8 symfun x143 1x1 8 symfun x144 1x1 8 symfun x145 1x1 8 symfun x146 1x1 8 symfun x147 1x1 8 symfun x148 1x1 8 symfun x149 1x1 8 symfun x15 1x1 8 symfun x150 1x1 8 symfun x151 1x1 8 symfun x152 1x1 8 symfun x153 1x1 8 symfun x154 1x1 8 symfun x155 1x1 8 symfun x156 1x1 8 symfun x157 1x1 8 symfun x158 1x1 8 symfun x159 1x1 8 symfun x16 1x1 8 symfun x160 1x1 8 symfun x161 1x1 8 symfun x162 1x1 8 symfun x163 1x1 8 symfun x164 1x1 8 symfun x165 1x1 8 symfun x166 1x1 8 symfun x167 1x1 8 symfun x168 1x1 8 symfun x169 1x1 8 symfun x17 1x1 8 symfun x170 1x1 8 symfun x171 1x1 8 symfun x172 1x1 8 symfun x173 1x1 8 symfun x174 1x1 8 symfun x175 1x1 8 symfun x176 1x1 8 symfun x177 1x1 8 symfun x178 1x1 8 symfun x179 1x1 8 symfun x18 1x1 8 symfun x180 1x1 8 symfun x181 1x1 8 symfun x182 1x1 8 symfun x183 1x1 8 symfun x184 1x1 8 symfun x185 1x1 8 symfun x186 1x1 8 symfun x187 1x1 8 symfun x188 1x1 8 symfun x189 1x1 8 symfun x19 1x1 8 symfun x190 1x1 8 symfun x191 1x1 8 symfun x192 1x1 8 symfun x193 1x1 8 symfun x194 1x1 8 symfun x195 1x1 8 symfun x196 1x1 8 symfun x197 1x1 8 symfun x198 1x1 8 symfun x199 1x1 8 symfun x2 1x1 8 symfun x20 1x1 8 symfun x200 1x1 8 symfun x201 1x1 8 symfun x202 1x1 8 symfun x203 1x1 8 symfun x204 1x1 8 symfun x205 1x1 8 symfun x206 1x1 8 symfun x207 1x1 8 symfun x208 1x1 8 symfun x209 1x1 8 symfun x21 1x1 8 symfun x210 1x1 8 symfun x211 1x1 8 symfun x212 1x1 8 symfun x213 1x1 8 symfun x214 1x1 8 symfun x215 1x1 8 symfun x216 1x1 8 symfun x217 1x1 8 symfun x218 1x1 8 symfun x219 1x1 8 symfun x22 1x1 8 symfun x220 1x1 8 symfun x221 1x1 8 symfun x222 1x1 8 symfun x223 1x1 8 symfun x224 1x1 8 symfun x225 1x1 8 symfun x226 1x1 8 symfun x227 1x1 8 symfun x228 1x1 8 symfun x229 1x1 8 symfun x23 1x1 8 symfun x230 1x1 8 symfun x231 1x1 8 symfun x232 1x1 8 symfun x233 1x1 8 symfun x234 1x1 8 symfun x235 1x1 8 symfun x236 1x1 8 symfun x237 1x1 8 symfun x238 1x1 8 symfun x239 1x1 8 symfun x24 1x1 8 symfun x240 1x1 8 symfun x241 1x1 8 symfun x242 1x1 8 symfun x243 1x1 8 symfun x244 1x1 8 symfun x245 1x1 8 symfun x246 1x1 8 symfun x247 1x1 8 symfun x248 1x1 8 symfun x249 1x1 8 symfun x25 1x1 8 symfun x250 1x1 8 symfun x251 1x1 8 symfun x252 1x1 8 symfun x253 1x1 8 symfun x254 1x1 8 symfun x255 1x1 8 symfun x256 1x1 8 symfun x257 1x1 8 symfun x258 1x1 8 symfun x259 1x1 8 symfun x26 1x1 8 symfun x260 1x1 8 symfun x261 1x1 8 symfun x262 1x1 8 symfun x263 1x1 8 symfun x264 1x1 8 symfun x265 1x1 8 symfun x266 1x1 8 symfun x267 1x1 8 symfun x268 1x1 8 symfun x269 1x1 8 symfun x27 1x1 8 symfun x270 1x1 8 symfun x271 1x1 8 symfun x272 1x1 8 symfun x273 1x1 8 symfun x274 1x1 8 symfun x275 1x1 8 symfun x276 1x1 8 symfun x277 1x1 8 symfun x278 1x1 8 symfun x279 1x1 8 symfun x28 1x1 8 symfun x280 1x1 8 symfun x281 1x1 8 symfun x282 1x1 8 symfun x283 1x1 8 symfun x284 1x1 8 symfun x285 1x1 8 symfun x286 1x1 8 symfun x287 1x1 8 symfun x288 1x1 8 symfun x289 1x1 8 symfun x29 1x1 8 symfun x290 1x1 8 symfun x291 1x1 8 symfun x292 1x1 8 symfun x293 1x1 8 symfun x294 1x1 8 symfun x295 1x1 8 symfun x296 1x1 8 symfun x297 1x1 8 symfun x298 1x1 8 symfun x299 1x1 8 symfun x3 1x1 8 symfun x30 1x1 8 symfun x300 1x1 8 symfun x31 1x1 8 symfun x32 1x1 8 symfun x33 1x1 8 symfun x34 1x1 8 symfun x35 1x1 8 symfun x36 1x1 8 symfun x37 1x1 8 symfun x38 1x1 8 symfun x39 1x1 8 symfun x4 1x1 8 symfun x40 1x1 8 symfun x41 1x1 8 symfun x42 1x1 8 symfun x43 1x1 8 symfun x44 1x1 8 symfun x45 1x1 8 symfun x46 1x1 8 symfun x47 1x1 8 symfun x48 1x1 8 symfun x49 1x1 8 symfun x5 1x1 8 symfun x50 1x1 8 symfun x51 1x1 8 symfun x52 1x1 8 symfun x53 1x1 8 symfun x54 1x1 8 symfun x55 1x1 8 symfun x56 1x1 8 symfun x57 1x1 8 symfun x58 1x1 8 symfun x59 1x1 8 symfun x6 1x1 8 symfun x60 1x1 8 symfun x61 1x1 8 symfun x62 1x1 8 symfun x63 1x1 8 symfun x64 1x1 8 symfun x65 1x1 8 symfun x66 1x1 8 symfun x67 1x1 8 symfun x68 1x1 8 symfun x69 1x1 8 symfun x7 1x1 8 symfun x70 1x1 8 symfun x71 1x1 8 symfun x72 1x1 8 symfun x73 1x1 8 symfun x74 1x1 8 symfun x75 1x1 8 symfun x76 1x1 8 symfun x77 1x1 8 symfun x78 1x1 8 symfun x79 1x1 8 symfun x8 1x1 8 symfun x80 1x1 8 symfun x81 1x1 8 symfun x82 1x1 8 symfun x83 1x1 8 symfun x84 1x1 8 symfun x85 1x1 8 symfun x86 1x1 8 symfun x87 1x1 8 symfun x88 1x1 8 symfun x89 1x1 8 symfun x9 1x1 8 symfun x90 1x1 8 symfun x91 1x1 8 symfun x92 1x1 8 symfun x93 1x1 8 symfun x94 1x1 8 symfun x95 1x1 8 symfun x96 1x1 8 symfun x97 1x1 8 symfun x98 1x1 8 symfun x99 1x1 8 symfun
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Walter Roberson
Walter Roberson on 26 Aug 2025
Ran in:
syms qd_t(t) [24 1]
qd_t = formula(qd_t)
qd_t = 
whos qd_t
Name Size Bytes Class Attributes qd_t 24x1 8 sym

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More Answers (2)

Torsten
Torsten on 24 Aug 2025
Edited: Torsten on 24 Aug 2025
You shouldn't use the way described here
https://uk.mathworks.com/help/symbolic/solve-semilinear-dae-system.html
to define a DAE system with 300 unknown functions.
You should directly create the mass matrix M and the vector f of the right-hand side that constitute your system.
Look at the examples on how to use ode15s:
https://uk.mathworks.com/help/matlab/ref/ode15s.html
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Tony Cheng
Tony Cheng on 1 Oct 2025 at 14:30

tau is not meaning time. it means torque. so torque is prescribed at t0 only, and at every time step in the time span from t0 to tf, torque is kept constant as at at t0. However, this is not right i think, since torque is the function of q and q_dot, which are different at every time step in the time span.

Torsten
Torsten on 1 Oct 2025 at 18:55
Edited: Torsten on 1 Oct 2025 at 18:57
Ok, I didn't know that tau is torque.
At the moment, you prescribe torque (I guess, differently) in every time interval [ cnt - 1 , cnt ] * t_h from the external simulation and keep it constant in each interval.
If you think that it has to be computed internally from q and q_dot, you have to compute
G_vtr = [ G_GSM1 ; G_GSM2 ; G_GSM3 ; G_GSM4 ; G_GSM5 ; G_GSM6 ; G_EE ] ;
F_vtr = [ F_GSM1 ; F_GSM2 ; F_GSM3 ; F_GSM4 ; F_GSM5 ; F_GSM6 ; F_EE ] ;
differently - thus express torque(1),...,torque(6) as functions of q1_dv,...,q6_dv.
But I'm confused: In your matrix equation, the external forces are explicitly written as F(tau,q). If tau is torque, for me this would mean that torque is independently given and not a function of q. But I have no background knowledge in the field of constrained mechanical systems.

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idris
idris on 17 Sep 2025
You do not need to type out all 300 variables manually, for MATLAB supports creating symbolic functions in bulk. It is recommended to use vector of symbolic functions, which creates x(t) as a 300×1 vector:
syms x(t) [300 1]
Now, one can access them as x(1), x(2), …, x(300), which correspond to x1(t),x2(t),…,x300(t)x_1(t), x_2(t), \ldots, x_{300}(t)x1​(t),x2​(t),…,x300​(t); thereby, providing the cleanest approach which works very well when formulating DAEs for ode15s.

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